On your last point, yes. I have used different levels in my Rickman over the years. Too much oil and there is excessive breathing from the forward breather pipes and seems to run hotter than the right level, my guess is this is due to inhibited flow. Too little oil, and it also runs hotter but breathes less, or even nothing.
Rickman say 6 pints for pretty much all of their frames, and when there is a sighting pipe this is consistent with the indication after the first running on fresh oil.
Lo and behold, 3.5 litres (6.15 Imp Pints) seems to work well in mine and is my choice for longer (20 minute) French or Belgian races!
For shorter (10 minute or less) UK races 3 litres (5.3 Imp Pints) seemed fine.
I'm reluctant to put less than 3 litres in, but that is just a bit more than Commando oil tank capacity anyway!
A fabricated oil tank for a Seeley (or modified Rickman) is likely to be around 5 litres capacity, but in use the oil content should be no more than 3.5 litres to allow 'breathing' space!
