I had (hopefully past tense) the same problem with my 2000 SL2. It
now has 200,000 kms on it, so I've changed the oil a few times.
I found to my surprize (even though it was tearing after a single use)
I could get away with not changing it until it was at the point of
ripping in half and it still never leaked.
A few oil changes ago I stopped by Canadian tire and bought some of
the generic nylon oil plug gaskets (1/2" I think - the OD is just
about right too). I installed two as they were a little thin. Over
the past 3 changes they have "moulded" to the perfect shape and
tightened up on the oil plug threads. They are working perfectly so
far.
BTW, my wife's 2000 SW2 with 70,000 kms on it doesn't have the problem
at all. It's still on the original plug and gasket - never torn,
never leaked.
I examined both oil pans carefully and concluded it must be related to
the fact that the SL2's oil pan stamping has a slight rise (not a bur)
close to the hole (where the "nut" is attached to the pan). My theory
is this causes the (very soft/weak) gasket to get over stressed before
the metal OD ring on the plug hits the pan. Even torqueing the SL2's
oil plug well below the spec the, gasket would tear every time.
Steve