As I said in my post, I'm not an NSR expert, but if the NSR have (oil) pressure fed mains, you'll also need to block those off to get an accurate picture of what's going on. Given the complete lack of pressure, I'm surprised the bike actually ran!
The centre seal will have a spring to help seal against the crank. However, over time the lip of the seal will go hard, especially if the bike has spent long periods of time stood idle, or has had fuel in the cases.
Fortunately for you, this is a great forum and there's a wealth of knowledge on here and I'm sure someone with specific experience of the MC21 will be along with some advice.
Regards
Mark
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