Overheating jigsaw puzzle

I’m soliciting opinions on the most likely missing event(s) or fact(s) in the following chronology:
(1) Dealer Service dept. tells us the serpentine belt needs changing. We look at it and let it go.
(B) About 3,000 miles later, car overheats with battery indicator light on dash (Okay, we blew it). We take it in for service. Replacement of serpentine belt and thermostat.
(III) While taking our money, the mechanic tells us there is still a slow coolant leak, suggests we put in a chemical sealant. We do.
(d) About 1,000 miles later, car overheats. We take it in for service. Replacement of thermostat HOUSING.

I forgot to say, the reason given for replacing the thermostat housing in (d) was that there were three cracks in it.

its easy to crack a thermostat housing when changing thermostat, and a small crack could go un noticed if the shop was loud when it was put back on. I know from experience that it makes a noise when you crack it while tightening.

hard to tell if he knew he cracked it or not, kinda sounds like it, but not for sure. it could have cracked after too.

was coolant leak at thermostat housing?

you should have had coolant leak fixed immediately. don t like that he recommended sealant if leak was at just replaced thermostat

Year ,make and miles would help
I’m not sure what you are asking but,
The cracks could have been caused by the overheating the first time and the mechanic didn’t see the cracks, or he was trying to save you further expense of the new housing…hence the sealant.
I would have prefered to replace the part rather than relying on a chemical sealant, a good sealant will cost almost as much as the part itself.