I've recently bought an immaculate Original Mod 6M marked Made in West Germany with an 01/81 date stamp. it shoots really well and I paid £50 for it....
Don't mess around with the power settings. Could be that you're anticipating the 'kick' at full power and your body muscles change which will change...
There are many different thread sizes for moderators that have been in existence for many years including variations of 1/2" dia, 5/8" and up to M28....