Are these caps are available to buy somewhere? Also the tv shelf is missing in the corner .... Looks like I have to re-do the seal as well. What is the best seal to recommend ?
the vent kit replaces the whole thing, you would remove the old crusty looking sealant, then use some new urethane marine sealant to put the new one down, along with pop rivets... the vent-only option is just the top cap. your call, but to me it looks like the whole thing needs doing.
Most people are now using a tv mount attached to the bottom of the upper cabinet. I ran across a Casita TV shelf brace today in the shop. I might have a shelf somewhere in the shop. Mine is for a C-17.
As John mentioned, you'll probably need to replace the entire assembly. The base will likely crumble if you try to replace just the cap. That was my experience with one not nearly so vintage.