Hi again Ross, never having owned a Rover 45, it is hard for me to answer that question...but it has been voiced before by mower repairers and some owners on this forum.
One area to look for is the engine shaft bearing, which on the original Scotties is a self-aligning type, the Rover having a plain bearing, which can cause problems.
As you mentioned, the paint finish is also questionable.
Best wishes for the clean-up.
