I am going though this with my 52 shadow after 40 years of sitting and a fresh rebuild...
I agree a GOOD cleaning with soap, water and a soft brush to get into the nooks and crannies from the mag cover to the rear stand knob is in order. Clean clean clean....
Then you need to take her for a short ride 5 miles or so around town and keep the speeds and the wind down so the oil will not drift far. Then take a small container of powder and blow it on the area that is oily and increase the powder coverage till you can trace the leak start. Spray foot powder works as does baby powder in a squeeze bottle with a spout in it like those used for dispensing condiments..
I found that oil on my rear wheel came from the following places:
Chain oiler... So I removed the fittings and plugged the hole at the back of the oil tank with a standard Vincent oil plug like the one found at the sump drain using the proper seal. Easy to do and it helped a lot and was not expensive to do. The needle valve under the oil cap will not cut the flow completely.
Compression release cable interface with the timing case.....I had the stock set up here and fresh rubber o rings 2 of them helped but did not solve the issue. What did solve the issue was the installation of the updated seal arrangement there. I think I got it from kemps or the VOC. Not expensive but it was fun to install as the timing chest has to be disassembled..
Push rod tubes...I had leaks at the top as well as the bottom and at speed the oil from there would easly reach the rear wheel and foul the brakes in 20 miles. This was the worst cause of oil on the rear wheel for me....The fix.....was not cheap or easy but it was straight forward. The heads had to come off and the seals at the base of all 4 tubes replaced with new seals once the area is cleaned and free of oil. Then the upper seals were replaced with Neal Videan:
nvidean@optusnet.com.au tube seals.
Oil lines on the top of the motor on the rear head just by the rear carb….All these lines needed new seals between the heads and the fittings and close attention to the line and the fitting interfaces. Some had to be re-brazed to stop the actual joints from leaking. Neal Videan seals were used and I did a terrible but serviceable job joining up the lines.
The quill at the bottom of the timing chest also leaked new seal and a bit of torque and that dried up as well.
Finally the breather also coated the rear wheel in its stock location…The fix for that was to extend the line so that it dragged on the ground leaving the oil there, and rebuilding the motor to reduce the blow by that blew the oil out.
From complete ignorance to a clean rear wheel took 2 years. The breather still mists a bit but that is fine hell at 60 years of age I will probably leak a bit too..;-)
Good luck and have fun. I did and continue to enjoy working on my Vincent.
Cheers,
Eric
;-)