From what I’ve read they are more efficient than the standard Oem seals enabling you to drop the preload/shorten the spring for a nicer firing cycle...
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...