If your talking about the insert pieces.
The two big ones; one unbolts with two screws, the other unbolts from the inside after removing the whole cover.
The one that is on the small cover by the shift lever, which is called the middle gear cover, is a real bitch. Interesting methods indeed.
Essentially the cover has a snap ring that pops into a hidden groove when it's pushed into place. Once in place there is no access to that snap ring so the insert has to be destroyed to remove it. The insert doesn't seal the engine, there is more metal behind it that is part of the overall cover and you dont want to damage this when taking the insert out.
I removed my cover and then used a die grinder to start punching holes in it being careful not to go through the second layer of metal behind it. There is an air gap between the insert and the cover.
Once I had enough holes so I could see what was going on in there I started removing metal until the snap ring could be pulled out in a circular motion kinda like unscrewing it.
When I installed the new Otec insert I used RTV instead of the supplied snap ring.
It's not that hard, just takes some patience.
The same procedure is used to replace the insert on the water pump cover as well.
Be sure to re-install the crush washer on the bottom bolt of the middle gear cover or it will leak.
Hope this helps,
Rusty
