A question of how to remove grease was asked and to this I say:

Try fresh vegetable oil. Just take corn oil, canola,peanut or what
have on A rag and massage the walls. The new stuff liquefies the old
oil and grease than after it is liquified it can be removed with any
household cleaner.
I have not tried this on on drywall but it works on hard surfaces like
stove tops and counters so it should work on plaster.

Good Luck!
H.R.