Leaking brakes, re-flare?

Common issue. A quick search for "leaking proportioning valve" on this site turns up three pages of results. Most every one comes up with one of two solutions: either rebuild the stock unit, or use copper flare washers (which may need to be annealed before use) at the connections.
When installing a new one, it doesn't hurt to disassemble it and clean it out- they have been known to contain residual machining debris. After installing and doing a preliminary bleeding, make sure you give the pedal a couple of sharp stabs to re-center the piston in the bore- they can hang up all the way to one side, which will make your brakes work like s***, and prevent you from being able to properly bleed out the remainder of the system.