Lawrence, thanks for the time and interest, I am going a bit around the topic because of past problems with this type of situation on this site..
The car was second ( or third) hand and had ca 20k on the clock, 1.6K series, recently purchased. We decided to fit an Apollo due to the oil frothing issue when using the car for long periods at high load. The tank was fitted and as expected we lost some oil pressure. The car was bought with some garantee and it was back at the dealer for this work. His opinion is that the car has run a bearing due to the low oil pressure due to fitting the apollo tank where the feed pipe to the engine has been replaced by an 'ordinary clutch pipe'.
We did not replace the pipe, we used what was there.
I am trying to establish if the restrictor can 'fall out' during fitting and exactly where it is in the pipe/tank.