Timing Flip-out

[Barkas]

Hi there. I have owned a (02) Mk 2 1.9 diesel lingo for 8 years now, had it from 2005, it had 14000 miles when i got it and now has 92000, and 2 or 3 times a year....every year....for 8 years..., while driving either in traffic or at speed, the engines timing slips out of sync for no apparent reason, lots of diesel knock, sounds just like the timing belt has jumped a tooth...enough to let the engine run but without power, i have to pull over and stop the engine, count to 10, then restart and away we go nice n smooth again for another 5 or 6 months when it will do it again. i think there must be an issue with the injection pump timing advance retard solenoid or similar, it seems to flip out at will. Is this a common problem and is there a easy fix or does the pump need to come off for recalibration / re-adjustment. thanks for any help.