When I first started riding, all the books I read stressed that one should check the oil circulation each and every time you start one of the things, particularly after a long lie-down. To make this possible, the Brit manufacturers pretty well all provided the scavenge oil pump return line in the filler opening. So you could start the bike, and at least see that the scavenge pump was working.
If you've had any "leak-down," common enough in periods of long storage, (long= >24 hrs) you will have a heavy flow at first from the crankcase scavenge, in any case it will settle down to whatever is being provided by the pressure pump to gutsville once the scavenge pump, always built to a greater capacity than the pressure pump, has caught up - after which time you'll get air bubbles with the return oil. Until that time, you may also get oil blowing out the breather, or smoking its way past the rings. Don't they mention this in the manual?
And if you don't see any return oil, the idea is to shut it down immediately if not sooner and find out why. No oil? No oil pressure?
With a Triumph, you can loosen the sending unit - at the front of the crankcase behind the timing cover - and look for a similar spewing of 30 or 40 wt. If it doesn't, pull the timing cover, and reseat balls in thg the spring and ball check valves on the oil pump with a punch and a small hammer. (They're behind the little square nuts on the ends of the pump cylinders. Watch out you don't lose the springs or balls!)
With the RE, you check for oil pressure by cracking the feed bolt in the center of the timing case. If 50wt doesn't haemorrhage out of there under significant pressure, shut down again and pull a cover plate off one of the pumps, and make sure the rotor's turning. If not, pull the cover and see which one's stripped - the timing pinion worm gear, or the pump shaft rack. NB: The timing pinion, once you've custom-ground a wrench thin enough to fit the nut (I've still got mine, after 40 yrs) is LEFT HAND THREAD! While you're at it, be sure to order another gland seal or two. The seal in the middle of the timing end of the crank. You might also check for eccentric movement of the crankshaft end, which will be an indication that your crankshaft assembly needs some serious realigning. This will wear seals in a hurry.
And finally, a story:
Inuit/Eskimo pulls into the Skidoo dealer in Remotetoyaktuk. Snopig is banging, smoking, barfing, and generally running like shit. Rider is really pissed off. Demands to see Service Manager, informs same that he almost froze to death out there, he's going back to sled dogs, Skidoo's a piece of dogbarf, etc.
Manager immediately sends serviceman to work on project, proceeds to placate irate customer. Mechanic gets thing apart all over shop floor, finally finds problem:
"Here's your problem, he yells from out back, "You Blew a Seal!"
"HEll I did, replies IC, I stopped at the hotel on the way in and had a hamburger. That's Mayonaisse on my mustache!"