Loose fitting oil pumps

[Big Ratfink]

I have heard of this problem - oil pump diameters being slightly under-size causing a possible air leak between the pump and the pick-up tube. I got to see this first hand myself today.

I have 3 stock VW oil pumps, 2 of the 3 are too small. My questions are:

1) when buying a new pump is there a way to know if it will fit right before you spend the money
2) If all you have is a loose fitting pump, are there any mods people are doing that will solve the problem?

[Marc]

Machine the pump body for an O-ring.

[Piledriver]

Note that an oringed pump really must be installed with the case on the halfshell, as sliding it into an assembled case without taking a chunk out of the oring requires lottery-jackpot-winning luck and a lot of case prep, and a slightly undersized oring.

I keep my eyes peeled for usable factory oil pumps. They tend to fit properly.
The stock pump is plenty big enough for ~anything.

Oversize "HD" pumps are bandaids for chainsaw wounds and seldom help anything, usually the opposite.