CHECK THE OIL FILTER O RING FIRST!!
Had this problem recently on '00 328 with 170k - replaced the OFH gasket twice! looking thru some of the posts one big thing to watch is the oil filter O ring- even in the pic above it is not installed right- I had done 8 or 10 oil changes and did not have any leaks till the most recent one- oil was pooling under the right hand side- just like in the OFH diy pics posted. Pulled it off again put a new one on and carefully torqued to spec, put back together- oil change and filter- STILL LEAKING POOLS OF OIL!! got feed up and took to local indy shop - if your in Sacramento CA area the guys a Stewarts Auto are the best - tech took one look at my filter O ring and said 'it's on wrong' the O ring should disappear inside the filter reservoir when it seats. IF YOU CAN SEE YOUR OIL FILTER O RING IT'S ON WRONG AND WILL LEAK DOWN THE BLOCK AND LOOK LIKE A FAILED OFH GASKET. Took cap off and looked real close at the 'groove' about 1/4 inch below cap lid and right above threads- there was a old O ring embedded in the groove!! pealed it out with a small screw driver- installed a new O ring, replaced cap- O ring vanished into reservoir!! NO MORE LEAKS!!
CHECK YOUR FILTER O RING BEFORE TACKLING THE OFH GASKET!!!