hi flanker .
when i see that kind of dirt i would say a filter cannot keep it all , means dirt is in your IP .
you have to fix everything to get clean diesel , means new lines and a new / different tank without moisture inside .
i have had a customer from denmark at my home 4 years ago , this G has has 770000km on its clock and has had loss power . he wanted to buy a motor from me , this day he piocked up a brand new getrag gearbox , so i made a test drive and the result was a surprise . in the end it was not the motor ...
he let made an IP overhaul and the G is still running perfect at this high milage .
if your 300GD does not have more power with clean diesel i would reffer to an IP overhaul .
mfg. guido .