My A4 is 21 years old, but has only done 47,000 km (29,000 miles), having been mostly stored after the death of its original owner.

Almost immediately after I bought it last year I replaced all the belts and tensioners as a precaution; while doing so I found that the serpentine belt tensioner I removed had excessive side play in its hinge mechanism.

When I ran the engine again I noticed there was noticeable oscillation of the tensioner, which could have caused its deterioration. After looking online for an explanation of this I decided it could be due to the alternator freewheel pulley, but my alternator had a solid pulley.

I found that no freewheel pulley was available for my alternator, so bought a new alternator and fitted it with a freewheel pulley.

This reduced the oscillation of the tensioner, but it still moves a few mm's back and forth at idle, although it is almost stationary if the rpm is increased slightly.

I am now wondering if the crankshaft vibration damper could be the cause of the oscillation; I didn't notice any damage when I removed it to fit the timing belt, but I didn't really examine it closely

Is a small amount of oscillation of the tensioner at idle normal, or could it be due to deterioration of the rubber in the vibration damper?

Does anyone have any idea of the life of this item, in years, rather than distance run?