Many have put the o-ring on the oil filter cap the wrong place. It sits in a groove about 1/2" below the flange. Some add an o-ring when one is already there. You just should have one. If it's been misshapen, just get another one...probably need to buy a new filter, but maybe dealer will have it by itself.
Same thing with PS reservoir cap. There is a $2 gasket that's replaceable. You have to trust me you have a gasket...it will be invisible, but if you use a knife carefully, you can get under it. Also, check the hoses beneath PS reservoir too...they leak all the time...new screw clamps should fix that up.
Oil from the filter cap is common(ish) because of what I said. Don't crank the cap down too hard either. I don't think you needed a new cap, but it won't hurt. I hope it's just the o-ring in the wrong place...make sure it's in the groove.
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Mangofy your E46!