IF its the diodes banks ( positive or negative ), having the replacements they are easy to replace at home. No need for special tools, just 1/4" socket and some other.

they can be checked in fact without dissasemble the alt, just using the VOM leads from exterior on OHM function ( middle OHM scale should be enough sicne they use to be on 100-400 ohms rate ), since diodes banks are accesible.

They can be even visible damaged/burnt.

Here I show how the diodes can be tested for positive bank. Same aplies for negative diodes bank but againts the alt case not the stud and swaping around the VOM leads.

( I can't recall right now if the positive lead of the VOM must be on stud or diodes to check the positive bank, but if doesn't work just flip the VOM leads around ).

All 3 diodes should register same value