Les, Biscuits are the most over rated product for wood work there is mate.
All they do is assist to keep the sides of two boards that are glued up level, you can do that with a hammer They do add some surface area so arguably a "little strength", but considering that PVA glue is stronger than any wood it bonds that is neither here or there.
I confess I have a biscuit machine that is near new
If you do require a locating method, dowels are the way to go.
The only "oily timber I have ever used is Teak, that was to make a record cabinet while doing my apprenticeship. I never wiped it down with anything prior to gluing and it is still as strong as the day I made it about 50 years ago. (I'm not saying to not wipe down oily timber)