I am currently using spar varnish, mineral spirits, and a dash of japan dryer. Apply thin coats with small pieces of lint free cloth. Scuff the buggers off with burgundy scotch brite between coats.
The truth is most any finish that dries thoroughly will work. The key is to use thin coats. Don't goop it up.
I would not use modern thick spray on catalyzed finishes on a ML. I would not use anything water based. Shellac is not good. Over the years I have seen lots of crazy stuff. The worst was used engine oil. The stock was black, stank, and the wood was ruined. Never use any type of mineral oil on a stock.
Lacquer is used a lot on furniture and cheap factory guns. IT is not bad as filler coat. Use Deft sanding sealer. Sand between coats. When the grain is filled use the top coat of your choice.
BLO takes forever to dry. You can add japan dryer. It just does not have any special qualities that make it worth using. For maintenance, If you want to put a bit of BLO on an already finished stock I won't argue. It look nice and smells good. After the BLO I suggest some paste wax.