You are right, I should go the whole hog but I don't want to spend any money right now!

Anyway, I swapped the coil stops and this has actually helped, but I still think it is an alignment issue. On the LHS there is a fair bit of play in regards to the plunger and coil alignment and it still being free, on the RHS there is a lot less room to move and it only takes a little bit of lateral movement to get the plunger sticking. For some reason swapping the coil stops has helped with this.