Regarding question 4 where people say thickening is never the problem:
Oil thickening was also time dependent. Thickening at 30,000 km was 2 times more when done over 21 months than over a 10 month period. (Change your oil every spring as I suggested before).
If a rarely driven sports car with with, say, a 7+ litre sump is driven only 7k klicks per annum, I see no justification to
change this oil "... every spring ... ". This recommendation cannot be made with out knowing how and for how long the engine has been run, also, the typical MB and or P approved lubricant has generous DP/AW to chemically "handle" the sitting.