Ms Peel has monitored those conditions to find the Norton is a pretty good heat dumper, not heat soaker, so as soon as the fuel supply reduced the temps start dropping and don't increase on [ugh] immediate shut off from hi throttle temps, such as a lost belt or chain or electrical fault or surprise road blockage. The hotter the engine on shut off the quicker excreted oil can drip off. This year I found the hotter my gapped tooth Trixie - the less smoke was seen, a few minutes of hwy cruise, only left invisable orders and slight smoke on nailing her, which also kept me in denial longer hoping rings or guides would self seal with more use.
Classic diagnostic tool is a leak down tester test to listen for where pressure escapes, carb, exhaust or breather and how much, but just can't be applied to a 360' twin w/o special provisions of essentially impossible brutal counter force, as one part of the test is move engine off TDC to move rings off possible good seal area, yet as soon as you do its suddenly a Norton torque monster to hold back and can't be stopped at just a tiny bit off TDC but tends to move enough to open a valve which nulls the test. Norton drum brake sure ain't up to it. Object stuck through spokes gets hard trapped and removal lets piston free fall. A case of beer offered to first video of successful procedure on our type engines.
Only way I know is too take down to bottom then work back up renewing most likely issues, one at a time or all at once, depending on how much faith and time and money on hand. I resealed Trixie's head and barrel twice before finding ring gaps bad by me haste to assemble with eager friend helping. If ya ever hear yourself or others say, yeah they all do that...
Throw yourself at the ground and miss!