Options for A/C Servo fix?

[LuLu]

I just bought my first Mercedes, a 1980 300TD with 300k and it is a great car. I've been driving it about 50 miles a day for a month and a half now with just one problems. The A/C Servo, the heat has only one setting "very hot" and I'm leaking about a pint of coolant a day. So what are my options to fix this? I've seen digital upgrades for $700-$1400, rebuilt ones for $300-$500, used ones for about $150 on eBay and a "upgrade" that bypasses the servo for about $100 (not a option because I want to keep her as original as I can). Is it the gaskets or the body, is it something I can fix? The rebuilt ones I've seen look like they have replaced part of the body with aluminum (I have access to a CNC Mill and good people). Thanks for the help