Most of my experience is with HD and performance machine calipers.
Never had to do my vic cause it is brand new.
Living on a dirt road I used to have a heck of time with the calipers on my 2004 hd. Sometimes I would have issues with the 13" six piston pm caliper on my shovel too.
HD's were made without any type of dust shield on the piston.
Performance machines are the same way. Because of that dirt builds up on the side of the pistons and causes some of them to stick.
When the performance of the brakes would start to go away I would pull the caliper, leave the pads in place and pump the pistons out as they would go with the pads in.
Then pull the pads out and pump the pistons out further one set at a time by blocking the other pistons back with spacers made from stuff around the shop. Then when I got the pistons out as far as I dared I would wash the pistons really good with chlorinated brake cleaner.
On the HD's the pistons won't come out too far. But that is no guaranty that Vic is the same.
I'd work a pair of pistons out wash them then pry them back and forth cleaning as necessary till they both moved freely and begin again on another set of pistons.
You have to watch you don't run the reservoir dry or over fill it while your jerking around with the caliper.
I'm guessing that Victory calipers are just like everyone else's and there is no magic involved but I honestly don't know, as my bike is too new.
If your pistons have enough build up on them it isn't inconceivable that they have dirt dragged into the orings just like your fork seals did.
Also keep in mind you could have a bad hose or connection.
Maybe someone at some time dropped the caliper while doing a tire change and damaged the hose at the swage fitting. My vic hoses are cheap looking things. Haven't had a problem with them yet though. Maybe they are tougher than they look.?
But it isn't hard to imagine one getting damaged if it did a free fall.
I use one of these when the brakes on anything are giving me serious fits.
If you can't find the leak any other way you can disconnect the line from the master cylinder at the master cylinder. Next pull a vacuum on the hose and caliper and see if it holds. If it does it is the master cylinder. If it doesn't, isolate the caliper, pull a vacuum on it and see if it holds. If not it is the caliper. If it holds the hose is leaking at the crimped on ends.
Air will go through holes too small for fluid. So it can be a bugger to find the problem sometimes.
Wish I could be more positive. I'd troubleshoot it out before I started throwing expensive parts at it. Especially since shipping is so high for you there. I'd guess your brake guy has a vacuum pump like that one and for a small fee would check your pieces for you. The pumps are a good investment because if you ever need to check a vacuum advance or anything vacuum related on a car or truck your set.
Those pumps are pretty cheap up here. Might not be the same where you live.
Anyway good luck. Again no actual experience on vic's unfortunately.