You may have trouble finding parts to renovate a Tech IV if they're needed. Linhof apparently made some internal design changes between the Tech V and the Master that aren't visible from the outside.

One that affected me was a change in the interior system for using the back adjustment knobs work (the four knobs that you loosen in order to move the back). One of the knobs on my Tech V broke when it fell off the tripod. The only reason it could be fixed was that Marflex happened to have the internal pieces for a Tech V back on hand. Otherwise I'd have been out of luck.

Bob Salomon could of course address this parts question with much more knowledge than I have. But even apart from that, having owned a Tech V and a Master, there's no way I'd replace the Master with a Tech IV. If nothing else that old system of handling front rise on the IV would be a deal killer for me. While you may pocket some extra money from a sale of a Master and the purchase of a Tech IV, you'll give it right back when you sell a Tech IV instead of a Master. And if you're like most LF photographers, it's not a question of IF you sell, it's a question of WHEN.