On my '75 Ironhead I've noticed A LOT of oil leaking from the transmission on the left side of the bike. I've ordered a new gasket and I am planning to remove the cover, change the gasket, and then refill with transmission+ oil from my HD dealership. I've got the service manual (finally) and I just wanted to reach out to see if there was anything else I should know. This is going to sound stupid, I know, but here are some of my main questions:

1 - do I need to worry about anything when I take the cover off other than a drain of oil?

2 - will I need to do anything with the clutch cable when I remove the cover, i.e. do I need to worry about air getting in the line (like bleeding the brakes)?

3 - If it still leaks after replacing the gasket - what's the harm in putting some sort of sealant along the bottom of the cover to stop the leak?

Here is a pic:
http://www.flickr.com/photos/67696148@N04/6289699172/http://www.flickr.com/photos/67696148@N04/6289699172/ by http://www.flickr.com/people/67696148@N04/, on Flickr

 

you will need to de-adjust your clutch cable, (no lines to worrie about) loosen the primary chain tensioner and be carefull removing the bolts,i am not sure how the clutch is set up on a 75 but that should do it, when you re-adjust your clutch there is a multi step process in adjusting it corectly just be gentle cover should pop right off

 

Be careful removing the drain plug. Steel plug in aluminum threads. If it is installed over tight the threads could strip. I use thread sealant on mine when i re-install, and i tighten it to just what i call "firm plus a litle more", probably 10 to 15 ft lbs.

After it is out and the cover is off check to see if a PO has installed a helicoil. Nice if it is already done.

The clutch cable is too short to allow setting the cover on the ground. I place an upside down bucket or whatever there as a resting place for the cover.

I would not use a silicone based sealant. Permatex Hylomar is one good choice and is what i would use.

When removing and when installing the cover it is important to keep it lined up. I cut the heads off a few 3" bolts same thread as the cover bolts, and use them as studs. Insert them into a few of the holes when pulling/installing the cover to keep it lined up. Also hang the gasket on them when installing the cover.

You will need the factory service manual 99484-78 to adjust the clutch.

 

if it continues to leak, putting sealant on the outside will only make a mess. The sealant won't stick where the oil continues to leak, even a small leak will continue to leak. Just make sure the mating surfaces are clean and everything inside too (oil will continue to seep from the tranny...you will need to wait until it has slowed enough that you can make everything clean and it will remain clean long enough for you to get the cover on)