William, 15/40 might be a little too thin, but as John said, clean oil is what you need.
To get to the sludge trap, undo the plate under the motor. It's in the flywheel and it looks like a bolt. Part # 1077-33 in this picture http://www.draganfly.co.uk/shop/pi-4563 ... egoryId=75
You might want to take the spark plug out and put the bike in 4th gear. Turn the back wheel until it lines up.
You'll need a tight fitting socket - 7/16 AF will work. It'll probably be very tight.
When you get the filter plug out, as well as cleaning the stuff in it, clean the channel above it as well. You'll need strong wire, or a drill bit.
Just some notes. Don't use a wrong size socket. If you round the head of the trap, you'll stuff it (big repair job, engine out).
It will be tight to undo, so lean on it a bit. Pull straight.
When you have finished, do it up, not over tight, just tight, with a small amount of low strength loctite.
Re the connector - do you mean the pipe outside the motor?
If so, you can't take the stud out, but you can take off the pipe by undoing the domed nut. You'll probably need new washers for either side of the banjo.
If you have cleaned all the oilways, don't forget to clean out the oil tank. There will be crap in there.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.