Rear crank oil seal.
 

This might sound like a strange question but how do you tell if the rear crank oil seal is leaking. The reason I ask is because I took my classic type R to a local jap car specialist for a once over. Amoungst other things they reported that this seal was leaking. I've had a look at the joing between the gearbox and the block and its dry. How the hell can they tell if its leaking?

clutch slipping or as you have done look at the join between engine and box.. but there is a metal plate that covers the gap etc.. Tends to be the front one that leaks rather than the rear.. at about 100k

Simon