With the support of a nation, the tank could be maintained as a devastating combat vehicle from roughly the mid 19th century onward. Far more important than it's ability to kill things, the Challenger 2 could turn battles and whole campaigns as the ultimate command vehicle.
As others have pointed out, fuel is not a problem. Diesel engines will run on almost any liquid hydrocarbon, though it might be hell on the filters, hoses, and gaskets. These could be replaced with natural equivalents (rubber, cotton, wool) but they would have to be serviced more frequently.
The main gun will be fun for a battle or two until you fire all 49 rounds of the standard load. It's possible shells could be manufactured for it, modern brass cartridges with smokeless powder begin appearing in the 1860s, but the materials and tooling to create them were known far earlier. Even black powder would work, but it would require extensive cleaning else it would foul the barrel. The lower pressure of contemporary manufacture shells would be a boon as it would serve to preserve the rifling.
It's possible to replace the main gun entirely with a breech loading cannon of equivalent weight starting with the Armstrong gun in 1855. The existing L30 gun weighs 1800 kg which could handle any number of mid 19th century heavy naval or field guns. The ability to move a heavy gun around the battlefield with impunity would be devastating.
The machine guns are arguably of greater utility on a pre-WWII battlefield to mow down infantry. They use 7.62x51mm NATO introduced in the 1950s. With examples to work from it would not be difficult to manufacture more. Depending on the era, the ballistics and charge might not be quite right. The biggest problem would be ensuring the ammunition is consistent enough to cycle to mechanism.
The commander's L37A2 is a variant of the FN MAG, a gas operated machine gun. This is fortunate as the gas system can be adjusted for the differing power of the locally manufactured ammunition.
The L94A1 chain gun, also using 7.62x51mm NATO, is even better for local ammunition if it can be kept powered. The external drive means it does not rely on the ammunition to cycle the gun. Any underpowered rounds will not result in a stoppage, the gun will fire as long as there is power and ammunition. As long as the batteries hold out, and the tank's alternator works, the chain gun will fire whatever ammunition fits in the gun.
Like the main gun, the machine guns could be replaced. The commander's roof mounted gun could be replaced with a Gatling gun. The coaxial gun, with only a small hole to fire through would have to wait for a single barrel Maxim gun.
Here's the real maintenance problem, the drive train: the engine, suspension, and transmission. Tanks are limited by their drive trains. Since everyone wants to shove more weight onto a tank, more armor, more equipment, bigger gun... tank drive trains are notoriously overworked. They have to transmit power to move 60 tons at 60km/h. Worse, they have to accelerate all that mass. This puts tremendous strain on the drive train.
Modern tank drive trains are cutting edge technology. They require careful and lavish maintenance. And they are irreplaceable. Even if you know how to fashion the parts, it's unlikely the metallurgy is available to handle the stresses and heat of a modern tank drive train, as well as the milling technology to meet the required tolerances. Locally fashioned parts might work, but at reduced performance and increased maintenance. Once something really vital breaks you have an immobile pillbox. A Challenger 2 maintenance schedule would shed more light on this, but I can't find one.
Careful driving of the tank, keeping acceleration and torque low, avoiding high speeds, and moving it around on flatbeds (rail cars being the only thing able to carry 60 tons) as much as possible, would extend life.
Here's where it gets really interesting.
The Challenger's rangerfinder, optics, and night vision would allow it to scout the enemy from thousands of meters away, through smoke, and at night. Even if the electronics failed, the backup optical sights are still of extremely high quality. Once those failed, replacing it with a good telescope would be valuable.
It cannot be overstated how bulky and awful military radios were up until even the 1980s. The Challenger 2 uses the Bowman system. Having a powerful, reliable, multi-frequency radio in a mobile armored box would be devastating. Even once the original radio failed it would have the space and power to carry a bulky Marconi radio. So long as there is copper wire, such a basic radio could be manufactured.
The Ultimate Command Vehicle
This is the most overlooked military advantage. Battles are won and lost on intel and communication. In an era where communications are still done with bugles and flags and runners, a mid-19th century commander who can be everywhere and know everything would rule the battlefield. Whomever has the Challenger 2 has the mobility, armor, and optics to scout the enemy with impunity, and communicate that information.
Imagine an army who has equipped their major units with basic, if bulky, radios. Their commander is in the Challenger 2 racing back and forth across the battlefield with impunity, getting first-hand information, disseminating it to their troops, and issuing orders in real time. They can scout any position, even though smoke, haze, fog, rain, and night. They can rapidly react to any change in the situation ordering their troops to react appropriately, concentrating where needed.
Even with no weapons, so long as the drive-train works the Challenger 2 can win mid-19th century battles.