Well, the old girl has been parked up on a 20 degree slope (Side to side) for 5 or 6 weeks whilst I use her as a tool shed whilst building her and her mate the Austin 7 a new wooden garage. I went to move her and she started with reluctance, firing on all of 1 and 1/2 cylinders. Checked that both cylinders were firing - sort of fashion, but one exhaust manifold was hot enough to burn skin (How do I know?) and the other was cool enough to hold.
Out with the plugs, hot side (uppermost of the slope) nice pinky brown colour, other side black as the ace of spades. Swapped the plug out for a known good one and went for a 5Km ride. No problems found, so deduced that oil was sucked into the downhill side during the 'layup period'.

Morale - Use, don't Abuse !
BobH