Early/earliest HP-41CV halfnut

[TallKey]

Addressing a)

Recently read an ebook* on repairing a 41.

Short of it is they use a Caig Deoxit product. It is applied to the battery side of the PCB key contact mechanism. The product allegedly can restore/wash the key contact. Each key location has about a 1mm diameter hole where this product is applied. It makes sense if a small amount of debris is the problem.

Never performed & never used the product they recommend.

Per their writeup a proper KB teardown and cleaning can only be performed on a Full-Nut.

*See thecalculatorstore.com, then the HP41 corner link.