I've currently got 16 Lima PGAs going through the wagon works to bring them up to basic running standard. Primarily this entails fitting Ultrascale wheels and Smiths instanter couplings, but I'm also taking the opportunity to replace the supplied steel weights with liquid lead. This isn't essential, but has the advantage that the wagons are far less likely to dart for the nearest uncoupling magnet - the only things left for the magnet to attract are the axles.
When fixing liquid lead in situations like this I use a 50/50 mix of Resin-W glue and water, applied with an eye-dropper until everything looks like a bowl of Weetabix swamped in milk. Those nearest the camera show what I'm aiming for, whilst those toward the rear are dry and ready to have the couplings added.