Main Bearing Oil Seal MK3

Rebuilding MK3 and Primary case side Crankcase doesn't have a grove for the circlip that retains the main bearing oil seal. At what depth or how can I install the oil seal correctly?
Bought this commando new but now believe the crankcases must be of the 1974 model which didn't have a grove for the main bearing seal circlip. Have ordered the 1974 type main oil seal and shim.
Don't have shop manual for a 1974 commando, can anyone provide installation instructions?
Thank You

The 74-850 and Mk3-850 cases would not interchange as there are a lot of differences. Such as the 74 chaincase is attached to the engine with 3 bolts and the Mk3 is held on with 4 bolts.

So if the circlip groove isn't there then someone machined away the cases, or maybe the groove is there but not visible under the old sealant. I have seen seals removed and re-installed right over the top of the circlip that was buried in the groove.

Installing either seal is about the same. Put some tape over the keyway so the edge does not damage the seal.

If there is a clip then just push the seal in far enough to get the circlip in place. It must be straight.

If there is no circlip as on earlier cases then there will be a shoulder to push the seal up against.

Either way some good sealant around the OD of the seal is necessary. I prefer epoxy. Jim

James, thank you for the information on the seal installation. (by the way Love the bronze exhaust port thread inserts, head steady, crankcase vent, and head work you did for me) The inner primary chain case is a new unused part that replaced the original that I had removed the starter from, to install a Drouin Supercharger back in my youth.
Not only does it not have a groove for the circlip, it doesn't have a shoulder to push up the seal to either. Just a straight through hole.
When I installed the seal I measured depth and tried to set seal back far enough so that the engine sprocket would not rub against it, came very close as sprocket rubbed slightly on one spot but not enough to cause any damage.
Did not use sealant around OD but will this time.
Prefer not to purchase another new inner chain case to find one with circlip and shoulder because of the expense involved, so thought I would take case off and insert seal till it is flush with outer flange on chain case that mates with crankcase.
Thinking that will clear both the crank bearing and engine sprocket, and epoxy it in place.
Any further suggestions? :?:

What type/ brand of epoxy do you use on OD of the seal?