SLK/R170: Removing the hard top
If you live in the UK then no rain is not guaranteed and the 'Sods Law' would almost certainly bring rain in some regions of the UK even in the middle of a heatwave.
Unless you are particularly familiar with the Vario Roof on an SLK I would leave it to a Mercedes Benz Independent/Specialist.
Identifying which motor is really a job for a diagnostic visit to an Independent/Specialist - I believe they are referred to a as a 'Star' diagnostic.


