[paynep]

1) Its called a bypass spring, I think they're the same on all 90's 2 and 4v engines, possibly part no 799.2.077.1A, available from dealers or my box of spares and it goes under the threaded bit that the oil filter screws onto.

2) Braking-wise no, but gyroscopic forces-wise probably using the right one only may be better for racing? I'm sure that one of the resident astro-physicists will be along to prove me right or wrong shortly........

Paul