I've seen that dip on all of mine, yes. Assumed purpose is related to locking/indexing stats (
process outlined in the factory manual...insert and twist clockwise to lock). I can new find stats w/bleed holes but haven't seen locking stats in the aftermarket, so...
These housings leak easily, usually due to a warped base. I clean them thoroughly, then patiently wet sand the flange on a full sheet of fine grit on a glass tile. Be sure the flange is flat and smooth, including the edges of the bolt holes. Set it on the glass and check it with a feeler gauge.
Installation involves a thin even coat of black or red (coolant safe) RTV both sides of a new gasket (
I use Fel-Pro*), left to dry overnite...now is a good time to re-paint the housing and clean up the bolts & mounting surface on the intake manifold.
Next day I apply a thin coat of spray adhesive to one side (
which will go against the housing), confirm the stat is pointed correctly against the flow (
spring towards the engine/manifold), bleed hole up at 12 o'clock if applicable, staying in place on it's own, using a bit of hot glue if needed, then attach the gasket, spray adhesive side to the housing, then position the housing on the also-cleaned-and-flat port on the intake manifold and bolt down....shop manual says 15 ~ 22 ft. lbs. Too much will just warp it again, so resist any temptation to go nuts, but don't wimp out, either. Remember the housing is steel but the manifold is aluminum.
This is all left to sit another overnite, -before- adding coolant and wrapping things up. Sounds like a pain, but again, these housings luv to leak and can apparently smell fear, so don't be shy about showing yours who's the boss.
Good luck w/it.
*
https://www.autozone.com/cooling-he...ket/fel-pro-thermostat-gasket/225119_199430_0
Ken