Hey Gareth, not really familar with the comp you talked about, but i have done shaft seals on york screw and centrif machines. be carefull after you pumped down that the valve is holding and no gas is returning. as already suggested an exploded view would be good for you. this your first seal change? if its a teflon "c" ring try not to touch the teflon as even a finger print could cause it to leak again, make sure you use loads of oil when sliding in the new seal. You say the motor is housed to the comp r you sure its not just the shaft housing. first job is to de-couple the motor and start from there. Shaft seals are actually supposed to leak a little bit off oil as it is actually the oil that creates the seal. But they do wear. how many hours of run time on your machine