Anyone in need of the main shaft seal for a Seca Turbo oil pump -
The seal is not listed by Yamaha as they only ever sold complete pumps which
are now obsolete.
I have managed to track down what appears to be an identical seal as used in
many Honda model oil pumps including the GL1800 Gold Wing.
The Honda part number is 91208-MN1-771 and the seal size is 11 x 15 x 3mm
If this seal has failed you will be getting oil flowing back to the turbo
via the return line filling up the exhaust when the bike is stored for more
than a day or two. I caught about 1.2 litres in six weeks from mine.
If you have the pump apart make sure the pressure relief valve on the pump
is working smoothly. I found mine was sticking and suspect it resulted in
over pressure at high revs causing the shaft seal to fail.
There is also a gasket on the scavenge line where it pass's through the oil
pan, the gasket is over a dowel tube and is pinched between the oil pan and
pump when the pan is fitted. To confirm this is not your leak you can
disconnect the oil line from the outside of the oil pan (leave the oil in)
and insert some 6mm OD clear hose through the pan and into the oil pump thus
by-passing this gasket. If the oil leaks from inside the tube its from the
pump and is probably the above mentioned shaft seal. If it leaks around the
outside of the tube then its the gasket.