disassemble the bolt to see if the firing pin really is broke....

I'd bet against it!

Also....the "possible" hairline crack should be magnafluxed to determine if it's a real crack. You might be able to determine if it is under a magnifying glass but magnafluxing is the best way. Not every gunsmith has one!!!

Try Dave Kliss at PTG as I think he makes new bolts for the Rem 788. It would have to be gunsmith installed and won't be cheap.

Frankly, if it was mine and the bolt actually was cracked.....I'd hang it up!....you can buy a used M-700 for less than the cost of installing (properly) a new bolt in your 788