whoa
Sorry but thats a new head gasket needed at least
I dont want to be the bearer of bad news but following your overheating problem you need to check out the head aswell.
triumphs use a wet liner so this is a big job to get done properly.
how long have you had the bike? and what has the dealer done recently?
how did you sort out the overheating? was it the cap?
Freddy
use a screwdriver not a 1/2" socket or come over and I will sort it for you. you could bring my rack back

and collect your Xmas card that I forgot to deliver