Oil leaking out of exhaust

[MickC]

Hello everyone, I have a CB900fz bol dor engine(79) in a 750 custom(81) rolling stock. After a long run the other week I noticed oil around exhaust outlet number 1# (bike has stock 4 into 4 pipes). I removed the exhaust and found oil over the exhuast outlet valve number1# (as sat on bike that is the one to the left hand side). It does not appear to be burning any oil - no smoke from the exhaust. Could it be the valve seal that has gone and if so does any one know how to repair it without having to remove the engine, or could the leak be elsewhere (and the oil being driven into outlet one by wind?
Any suggestions are welcome, I'm not an automotive genius but I'm not afraid of getting my hands dirty and i know what a spanner is.
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[Frost]

Exhaust valve stem seal.

[MickC]

That's what i was thinking, any ideas on how to remedy it without having to remove the engine (its bloody big and heavy!) ?. From what i've been told you can't take the head off whilst its in the frame (the frame is the same as the other 750's of the time apart from the seat rail set up).
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Previous: CG125,XS250 (converted to 400),Z250A, GPZ550, Norton Commando, XS500, 78 Laverda Jota, GPZ1100,Harris bonneville, XV750 (mono shock),TR1

[Frost]

Yup the head has got to come off and the valve removed using a spring compressor. You might as well replace them all, lap the valves and do the clearances too. An easy afternoons work i should think.