The TOS cast writing books about working with Shatner was a cottage industry for a while. I'm still waiting for the stuntman who played the Gorn to tell all. ;)

I'd like to think Shatner and Doohan patched things up before it was too late.

They appeared on the TV Land Awards several years ago, along with the rest of the TOS cast. (Except for DeForrest Kelly of course.) IIRC, it was Doohan's last public appearance, not that long before he passed away, and it was distressing to see how frail he was at the time. Shatner was the one helping him walk offstage.