These are almost service parts on The JTD's they are used by a large number of car makers with the torque produced they suffer in the same manner as the DMF...Hello Longprest,
1 is there any visible wobble when viewed from above or side on? (Engine running!)
2 are there any cracks/ perishing or splits in the rubber centre; try and see if you can get a look at the rear - although some versions of this part have a metal backing plate, but if not, check for same fault there.
If the answer to any of the above is yes, your bottom pulley is due for replacement.
Hope that helps