To be honest there are loads of conflicting ideas, it seems some can use just a 4.7 ohmn resistor and that on its own will cancel the light. I took mine originally to an auto electrician he put a little black box for a BMW that contained two resistors either side of a diode, it cleared it for a few days, then came back on again - dont know the value of the resistors they used. I have googled the issue, and there do in fact seem to be a lot of problems linked with the early BMW's.
Their fix is two 100 ohmn resistors either side of a 1n4001 50v 1a silicon diode, this seems to put the light out in most of cases listed.
I wonder if thats worth a try, it does seem to be very much trial and error with the seat sensor.