[Fot] When do you replace a rubber lip seal?

[Steven Belfer]

I'm rebuilding a TR3 motor with 20 races on it.  I know that's a lot.   
It's back from the shop and ready to put back together.  It's got one  
of those rubber lip seal conversions.  It didn't leak more than it's  
supposed to, ha ha.   Is this lip seal a part that should be  
replaced?  Now would be the right time to do it but it looks good and  
I'm on the fence between putting it back in the car and getting a new  
one.   I've heard there are two types of these seals.  How do I know  
which one I've got?  There aren't any markings on it.
So...

A, can these things last 20 years?

B, What should I measure to figure out what I've got

C, Who sells the best ones?


~Steve