from reading your other post, iirc, it was suggested to test the coolant system. But both tests would be of use i imagine. Looking at your pictures it does look like liquid in the bore. Could be fuel tho? The steam out the exhaust could well be water getting in, as mine did, through the rusted section behind the back box/joint to connector pipes area and running down into the exhaust and just sitting there, i an fairly certain the pipes are seperate up to the back box where they join in the silencer. The leak could be any number of the omega usualls. But, put them all together and does make
HG more likely. Have you changed the oil recently, while you have been having these issues? If so and the oil is fine, ie good texture and thickness, still thick and good colour, ranging from gold yellow to dark brown, then the hg is fine imho. But if its milky, frothy, thin, grey, chocolatey, with white mayo deposits then you have water in the oil seeping/blowing past the piston rings and into the sump. I would drop the oil out and see whats its like.
I have read on here of bottle caps blowing off and bottles destroyed by hg failure at 60mph. So still some more tests to do before you dive in as you say.
Maybe have a look at the dipstick as a clue and drop the oil when you get it home. Do that before you spend money on test equipment maybe? Cheaper and if there is no water you can fill up with fresh oil and all the better. Hth