The only engine related problem I know (not counting the old Vlach ignition) is lubrication of the front seal. Easy to fix by a drop of oil between prop hub and crankcase every now and then.
26cc conrod problems were solved three years ago. Old engines will benefit from a couple of shims under the head.
LE is essentially a prosport, with bling colours
MVVS engines need premium fuel 91 PON or better with high quality oil. (.)  Lower grade fuel will very much shorten their life expectancy, unless you reduce compression ratio by adding shims. If you follow the manual, you'll be good.
Oh, before I forget. They need proper cooling as well. All mechanical repairs I had so far were heat related.