load sensing dual proportioning valve

G'day folks,

Got an 85 dodge Caravan and doing the brake lines. Got 2 brake lines off the load sensing dual proportioning valve ok but stripped (might be able to tap it) the threads on another & one is still stuck solid (so far..).

Can the stripped thread be fixed? Helicoil maybe or drill it out something.. Dealer sez part is no longer available & only one that is the same is in 84-5. Don't imagine it'll be easy to find a good one.

Also dunked the whole thing in wd-40 for a few days to try to free up the bolts & maybe messed up proportioning valve (guessing it has seals) cos wd-40 is petroleum based?

Dunno how that thing works, looks like it has a lever type setup that makes contact with looks like 2 electrical points, or contacts.. but course no wires go to it.

Wondering why the brake line bolts are 2 diff sizes but both use the same size brake line? 2 are 3/16 (think) & the other 2 are the next size up

Any other alternative to using the original load sensing dual proportioning valve? Maybe a couple of adjustable ones from simmit racing? Not sure if (or why?) I have to stay with the load sensing setup figuring cars never had 'em before.