I have used Surfex HD from Bilt Hamber in my ultrasonic cleaner for a few years now the parts need to be free from most of the usual crap that accumulates over the years. I use the same product in my parts washer to soak the bad stuff away. In the ultrasonic I set the temp at 60 and clean for 30 mins. If things are really grotty I sometimes take them out after the first 30 mins and use a scriber or small screwdriver to loosen stubborn bits in the crevices and then do them again. 5% Surfex by volume has been good for me so far.
Ian