I love Rail-Zip. Not only has it fixed the dodgy window switches on my car, it's also pretty good on model railways :-)
A small drop on the inner flanges keeps the pickups clean, and it is really effective for cleaning rails.
But (you knew there would be a but, didn't you?)
Diesels and tender-drivers with traction tyres. What to do? The two simply are not compatible - any drop of Zip on the rails and the tyres pick it up, and slip mightily.
p.s: gotta love Setrack. Planning out the new layout, son Pete decided to plug some setrack together and play trains. Great fun, reminds you what it's all about.
Guy