Well, I replaced the rear most rubber lines, then started her up. Suddenly I had way more foaming bubbles coming through my clear line. What?!? Went back and looked for leaks. Nothing at the new rubber lines, BUT there was wetness at the top of the tank where there hadn't been before. Guess my suction tube lines were probably rusty and compromised enough to let air in as it cooled down. Once I put a little strain on them by changing the rubber lines, the gap got bigger. Now it won't even run without priming the filter every so often. And a milkshake is coming from the tank.
Tough way to find the leak, but at least I found it. There was no actual weeping before but I didn't disturb the lines that much coming out of the tank, so they had to have been pretty corroded... a little movement in getting the new lines on was enough to finish them off.
The part is now 7-10 days from the warehouse, and then UPS hopefully gets it to me quickly.
If anyone is looking for it, its this one:
7724060190 | TUBE SUB-ASSY, FUEL TANK SUCTION |
Bolts onto the top of the tank, two little barbs come out of the top. Dips down into tank, and a plastic filter sits down in the bottom of the tank. Probably pretty dirty by now too?
And so now I get to drop the tank. Luckily I just filled up the other day, so there's probably about 70 litres of fuel onboard. LOL

Oh joy. I'd like to say this saga is likely solved, but I won't promise anything yet.
I'm pretty sure a lot of folks with older rigs have air leaks but just accept a bit of startup smoke as normal and go about their day. Maybe that's what I should've done?