Don't use Brasso if you think the wood finish may be shellac.
The ammonia content in the Brasso will soften the shellac and you'll have a mess as you try and rub the stock down.

Cheap Ammonia household cleaner is an excellent brush cleaner for shellac use.

I always just used Linseed oil and a small amt of Mineral Spirits to clean old wood finish.
I'll try the addition of a bit of vinegar to the mix.
Thanks for the tip!