I thought I read in that RZ thread someone DID say they put it on the inlet.  That's not how the metal one I gave the part number to is designed.  It goes in outlet. 

Here is a post from GFrench mentioning he installed an external check valve since his pump leaked.  You can see it in the video.  Looks like a metal one? 

yamaha-enduros.com/index.php/forums/rest...-one?start=170#69536

Thanks MarkT
Yes I seen it, I have ordered the part number you gave me from my local yamaha dealer, will look fwd to a fix I hope.
i may try and see if I can squeeze it in the side casing with the pump, but wont know till it arrives

I got the check valve and did a temp set up to see if any weeping, 3 days later and no weep, so I have now installed it and managed to get it in the oil pump casing
Ive set another test pipe at carb end to check again for weeping in a weeks time, if ok will button it up

Thanks go to MARKT fore knowing the info on the external valve and for giving me the info. I would of been stuffed without it, thanks again for your help.
  

GARYDEAN do you have the part number for the check valve? Somehow I missed it, would like to get one to keep on hand encase any of mine decide to not cooperate. Thanks, Tony

Hi part number is 8CH-1316A-00
£27 in uk and it worked. I removed the old spring n ball from the pump
no more smokey starts!! It got to the point of wiping the area out with smoke, hopefully now all back to normal

Thank you...