A whole tin (500) is a good idea, this gives the piston washer time to self-size, unless you have sized it too small in which case nothing is going to help.
Lube should be a stripe of moly grease at the back of the piston and the merest smear on the piston seal, and use a small paintbrush to paint a smear on the spring (I get the kids paintbrushes from Tesco, a couple of quid for 6 or so).
Good luck!