Spring may be in correct holes but if it is weak it won't be able to compress the fluid back into the system.

The shoes may not be keyed into the ends of the WC pistons quite right.

The e-brake lever and self adjuster bar may not be in the proper slot (not quite far enough down).

DO NOT remove the p-brake cable at the hub! You will never get it to go back on without removing the hub again! Slacken at the balance bar (end of handle lever near driveshaft support) and remove there if you have to remove it.

Check that flex-tube for fluid is OK. If you don't know when it was last replaced then do so (they tend to swell up over time and hold pressure at the cylinder and/or crack and fail, suddenly).

Re: the square stock key. Clean out the keyway in both the axle and the hub (and really clean for the hub). Tap the key into the slot in the axle. I then lube up the axle and hub with anti-seize (not a LOT) and carefully slide the hub on. If the end of the key disappears, you may need to do the balancing act of tapping it in after introducing the hub to the axle... Or you can intentionally use a punch to put a small burr on the side of the key that goes into the axle to give it some "bite" to prevent it from slipping out after you tap it into te keyway on the axle.


--
Mike!