MINI went through something like 5 design changes on the tensioner.... If the two that are in your hands are not the latest.... They are both suspect...
Tensioners can go bad if the internal spring relaxes, resulting in the chain not getting the proper tension...
Tensioners can go bad if proper oil isn't used or the oil change interval isn't maintained... They can stick or bind up from oil contaminants and not apply the proper tension.
Tensioners can operate at the wrong tension if the oil level isn't maintained or the oil pressure drops... Even on the latest version....
MINI doesn't publish spring tension on new tensioners.... Measure the tension on a new version tensioner, and as a starting point, compare it to the two in your hand... That would give you a good indication if the two are good or bad....
MINI went through a number of length changes with their various versions... Some are shorter... Some are longer...
Even with a new latest version tensioner, if the valve train assembly has been damaged, even the latest version won't do much for you.... They all work together and need to be within specification..... In other words.... If you have holes in your tire... Don't expect new air to do much good....
