Odd thought. I was a MDS fan and other than the carb on an early 148 never had any problems. But I just don't remember ever seeing a 108. I thought the range went from 78 to 148 with no intermediate engines.
Are you sure you have a MDS 108?
The 148 is a great engine but it does not like high nitro fuels. I ran mine on 5%. They also take a fair bit of running in.