Lovely saff you've got cossienut think it's amazing you've owned it for 21 years I hope to own mines that long.

Op I wouldn't worry about the oil I experienced similar recently on my 10k fully rebuilt engine, hadn't used a drop in ages until one night I went to a car meet my mate took his Impreza which pretty much resulted in a constant high speed race there and back and it didn't half use some oil there. Topped it up and hasn't used any since.

I'd defo look into getting yours live mapped, msd work wonders on them and are great at finding hidden gremlins that you weren't aware of.