Front brakes won't release

Like everybody else is saying, my guess is that the caliper pistons are not able to force the fluid back into the reservoirs.
My first go-to would have been pushrod length, and
Second would be plugged compensating ports, and
Third would have been the square-section caliper seals, in corroded grooves.
But since this is an ongoing problem, My question is in regards to plumbing;
In the factory system, the front brakes are plumbed to the REARMOST chamber, via the "top" of the Combination valve, which is the opposite end of the Proportioning part, and thru an OPEN port without a residual valve.
Jus saying.