I actually own one Hondamatic CB750. It's a 1978 model and has 12,000 on the odometer now. No problems ever with the transmission.

 

Funny you mentioned that about the Choke housing. The same exact thing happened to me. I narrowed it down to the choke then finally found frozen water in the choke tube housing. I went with the silicone and carburetor cleaner as well and have not had any problem with it to date. I first picked up my new Rubicon in August and didn’t have the problem until our first freeze in November. Glad to hear I wasn't the only one to suffer this problem.