I’ve had pretty bad tricep tendonitis but I’ve gotten rid of it, it took couple of things:
I stopped doing any heavy tricep work for a week (for me this is mostly compound pressing and dips, I don’t bodybuild). This helped alleviate immidiate pain.
Found out what didn’t hurt: suprisingly I was left with dips. Did them for few weeks, started adding weight, introduced overhead presses, and after 8 weeks back to benching.
Biggest single thing for me was taking a critical look at my technique. What I noticed was that I had a tendency to start the concentrics of my pressing movements “with my elbows”. Trying to be as explosive as possible, putting huge stress with every initiation of the lift and doing high volume presses and benches was what caused the problem. I practiced starting the lifts more evenly (all the “bench with/from your lats” etc. powerlifting cues started to make sense), and now I’m virtually pain free.
But, I don’t do any isolation work really, so I can’t comment on that.