No not normal !
A small amount in a few spots just to hold the rubber seal in place would be acceptable.
That or some heavy grease would have worked.

O ring grease for o rings, silicon is excellent for gutters, shower screens etc not engines / gearboxes it has a habit of going where you do not want it to go eg oil galleries and bearings.

loctite 515 flange sealant is what i would use (if anything) in this senario.

It was the cover right? not the plug?

not a biggie really, the main thing is the o ring could have been damaged so they should have fitted a new one and made sure they didn't pinch it again

i use hi temp silicone sealer , just a smear and leak is gone