[brucep]

It is EXCEEDINGLY rare that a Subaru caliper gets 'sticky' piston. I have seen MANY occurrences of the sliding-pins getting sticky....and some instances of the brake-pads themselves getting rusted into the holders so they stick.

Judging from your photos, you purchased a LOT more than just calipers... you have complete units there. (including the sliding-pins)

I guess what I am saying is that, if at all possible DO NOT open up the hydraulic system. Opening up the hydraulic system brings with it all kinds of additional work such as bleeding at all four wheels.

Instead, you may be just dealing with some sticky sliding pins. In that case, just replace the caliper 'holders' (which includes the sliding-pins) and reuse your old calipers.

Personally, I just free-up my existing sliding-pins and grease them well. They will continue to work for many years. This also saves me from removing the rotors. (and the only cost is my labor to remove and fix the sliding-pins )

 

[brucep]

Where have you heard this opening the hydraulic system opens up a lot of work? Anytime you do a brake job you should change the fluid. Most DOT 3/4 fluid only last for about 2-4 years. As it absorbs moisture from the air. It's just lazy and poor work ethic to not change the fluid and to just compress a piston without opening a bleeder. Generally that's where I see frozen or sticking calipers is from lazy people who dont change brake fluid. It's so easy to change. Even the $10 one man bleeders on Amazon work well enough. Spend another $40 and you can get a power bleeder.

I do not need to "hear" that opening the hydraulic system opens up a lot of work... I know it from over 30 years of working on brakes. In many cases, the bleeder nipples will snap off. or the years of roadsalt will have corroded things to the point of further destruction whilst attempting to disassemble. (metal pipe connectors, holddown bolts... pretty much EVERYTHING underneath a car is layerd with rust)

Also, you are making a LOT of assumptions regarding how I work on my own vehicles
*)First of all... I live in Vermont where the roadsalt destroys rotors before the pads wear out. (Then the rusty rotors wear thru the pads quickly)
*)Secondly, I DO INFACT own a vacuum-bleeder and replace fluid every 3-5 years (This may be the reason why my calipers last the life of the vehicle)
*) Third ...I have learned to remove the bleeder nipples and add teflon-tape to the threads when the vehicle is 'new'. This helps keep the nipples from becoming corroded inplace between bleedings AND it seals the vacuum-leak around the threads when vacuum bleeding.
*)Finally, I have replaced 100s of brake-pads and know enough to use metal-based pads in Vermont which help the rotors last more than 2 winters. (more aggressive on to reduce rust formation on rotors)