Originally Posted by rao
After much discussion, it turns out that there are TWO filters inside of the banjo bolts that are at the entrance to the oil feed pipes
The filter in the oil feed line idea is similar to how some auto trannies have a filter and some don't. The filter is supposed to save the turbo or tranny in case contaminants are circulated in the oil. The problem is when the filter gets clogged it does more harm than good and a vicious cycle starts when lower oil pressure causes more contaminants to be added to the oil causing the filter to become more clogged, etc.
From what I understand Toyota auto trannies don't have filters and they tend to last much longer than most other trannies.
Also, Mitsu doesn't use filters in their turbo oil feed line and their stock turbos easily last 100k + miles.