You would not want a gasket between the carrier and head as it would affect the clearance between the cams and hydraulic lifters. I'm guessing the sealant is an anaerobic type and that the carrier has gaps that an anaerobic sealer(cures without air) won't fill or cure. Regular RTV (Room Temperature Vulcanizing rubber) would be risky around the oil passages. If you used a rotary disc tool it could have removed enough material (aluminum) to create poor geometry of the mating hardware.
The surfaces need to be clean, flat and dry. No residue from the old sealant! Then wipe down both surfaces with a non-petroleum based solvent. (Lacquer thinner) Do not use mineral spirits! No sealant will bond to oil!
GM used anaerobic sealant on the Brazilian 1.8L and 2.0L cam carriers, their sealant is probably made by Loctite- could be better than the Volvo stuff???