Not that I'm aware of. Uban myth from the UK restrictions maybe. LC models had washers but don't think they went to the US.
More likely on a 78 is your high speed coil is failing. Check the stator resistances.
The 78 cdi uses 2 Coils one for low rpm the other for high. Known as a 7 wire system amongst owners. Yep 7 wires between the cdi and the mag.
The approx point where the system switches over between Coils is 6k.