Any suggestions how to remove an aluminum cap?

[suha]

As the subject implies, I've ran into a problem. Or rather, my friend has. He's got a 1975 GL1000 and because of reasons he hasn't changed the oil in the final drive. Ever. I'd like to think my reviving/restoration project has inspired him to take better care of his bike, but either way, he recently decided to have a look at the oil. The problem is, the refill cap has been rounded off by a previous owner and the socket wrench couldn't get a grip. Today, we removed the mufflers to try to saw a grove in the cap. It was surprisingly easy to saw. The aluminum was very soft. So soft, that when we tried to use the grove, the metal just gave way where force was applied. The cap wouldn't budge. The only solution we can think of now, is removing the final gear cover (if it can be done) and then try to get the refill cap out without risking getting debris into the final gear. Does anyone here have an easier solution?

[Rambozo]

You can usually walk them out with a punch. That cap is a very soft die cast part that Honda has been using on almost every motorcycle they have ever made. Always use a 6 point wrench on it. The wrench Honda supplies in the tool kit is ideal as it has sharp corners and no chamfer. Many sockets have a chamfer to make it easy to get on a fastener, but the hex on those caps is so short that most sockets won't get a good bite on it. You can grind off the chamfered portion of a socket to make it work better. An impact wrench or even tapping the handle of the tool kit wrench is often better than pulling on it with steady pressure.

[cfairweather]

Replacement caps are easy to find as these are the same as the CB750 tappet covers.