Im no expert…nor am i a repairman, but i have dealt with this a few times.

heres a link to such an issue on the martin guitar forum. Smarter folks than me.

https://umgf.com/sticky-finish-on-79-d28-t227572.html

I believe pledge is silicon.
What it does, to shine stuff, is leave a micro coating that appears as a ‘shine’, as it ‘fills in’ tiny scratches, etc.

I am guessing that the surface is nitrocellulose, not a polyurethane or other cured plastic finish.(the latter 2 types should not have softened).

No, its not meant for metal, but will remove prints, etc.

Assuming you don't want to refinish, per the link above....

try the recommended Nomad polish....(haven't tried it myself). (I have used the fine, tan bottle macguiars car polish, the very fine and the glaze...great stuff)

if not....

I suggest getting a clean, soft LINT FREE cotton rag and thoroughly dampening it with naptha. (Lighter fluid) Silicon is notoriously difficult to clean.

Id lightly use the damp rag to wipe, NOT RUB, the neck. Might take a couple of tries.  A few days in between...

It may take a very long time for the finish to not be tacky. Bad news…it may not if the silicon has thoroughly penetrated the finish. 

Naptha should help. It wont hurt, provided that you lightly wipe the finish. Do not use denatured alcohol, as it can cloud the finish.

Id leave the instrument out of the case, if you are able to do so safely. Exposure to circulation of air may help. Hardening, depending on a bunch of stuff, as well as relative humidity may take months.

Good luck.

Thank you Steve.

Naphtha sounds good. Google says either mineral spirits or a 50-50 solution of white vinegar and water can remove a build-up of Pledge.

Mineral spirits is safe for nitro lacquer and polyurethane finishes, so maybe go with that. I think acidic vinegar can be bad for lacquer.

Pledge should never be used on an instrument. Most grocery store furniture polishes should not be used.

Perhaps the biggest problem with silicone-containing polishes is they prevent refinishing later on.

Good luck.

I would not assume the banjo's finish is nitrocellulose. If the banjo has a brand name, do research to learn what the finish might be.

Naptha

If you use the white vinegar and water, just make sure you don't get the vinegar on nickel parts. It will tarnish nickel very quickly. Naphtha is a good idea.