it seems that there is very little information about the differences between the CD40 and the CD40 MKII
The MKII seems to have a different Transport Assembly, both models are designed around the highly regarded TDA1541 DAC. You would need to locate the Service Manuals for both model if you want to detail out all of the differences
The key to having vintage CD Players is - are replacement transport assemblies available? Sooner or later it will likely fail - Chris