Richard ,I don't think the plunger box as any more vices than the s/arm box which I've just rebuilt . I'm no expert but I'd check the selector dogs for wear ,likewise the cam plate ,that the cogs move smoothly on the respective shafts ,don't forget the shim on the layshaft behind the bushed pinion .When you come to reassemble camplate fixed to neutral position. Someone posted a beaut of a tip which I always use to keep the selector dogs in place , simply use an elastic band ,ex postman discarded ones are just right and its then quite easy to reassemble . Hope thats of help, Bob