Like written the good glow plugs are BOSCH : 0 250 201 032 / 80010
If one broke off in the engine that's mean your injection system was not properly tuned : leaky injectors or bad advance or bad release pressure.
VO tends to make the nozzles very dirty and make the spray pattern bad the more you use it.
Like i wrote yet VO is a way thicker ,and so slower, when you inject it (even very well heated) that mean you need to retune according to it's own properties.
With normal fuel the correct advance on a d24 t is 0.87 to 0.95 when checking and works good at 0.95.
with VO it's very different.....
Try this yet :
http://www.forum4x4.org/threads/8941...A-GAZOIL/page5
VO needs to be heated and filtered VERY WELL !!