I back up what Steve has said. I have managed to repair two 405's, one very recently and my main concern being blown thick film circuits was sorted by a visit to Huntington where replacements were available. You need things like a Variac so you can apply power slowly while looking for bad offset voltages on the output and of course struggling electrolytics.
Make sure you replace R7 and R8, 3.3k between the 50V rails and the 15V zeners D1 and D2. The resistors have a nasty habit of going open circuit and this causes no end of problems. Not entirely the resistors fault as in the 405 they are being subject to over dissipation so you need to replace with 1W types.
I am also lucky in having high power 8 Ohm non inductive loads and a distortion measuring test set, very rarely used but a nice to have when dealing with something like the Quad 405.
Here are the notes I took which may be useful to anyone working on a 405.
http://www.g4cnh.com/public/Another_Quad_405_repair.pdf