First off, a VS is an old printer. Decide how much you're willing to invest in this before you get too far. Then start with the basics - Cap top, damper, wiper and wiper scraper - Go with OEM parts. Then if you still have problems, it's likely the print head, but you've already replaced the accessories that should be replaced when you do a head. This much will probably run you about $3000 - $3500 if you have a tech do it.
After that, I've seen a lot of VS printers with ink flow problems in the rest of the ink train - mostly choke valves or cartridge holders, but it could be any joint or O-ring in the system. It can be tough to track down.
Good Luck
