How to replace seal and orings in pump and get inpeller back on

High side is just an O ring. Replace it with the same size.

Yes you can replace the seal only,Its only a bag in there that attracts moisture, do you need to replace it not really,Just replace the seal and ensure there is no leak.But if you open the system you ll need to draw out the air before you refill with freon

You can always try Leslies.com It has almost any parts you want and they will ship to your home.

The oring on the headvalve/piston should be replaced. You can use any oring that fits snugly on the groove. Factory oring is vinyl but use black rubber oring, works just fine. Most likely place to find orings is Lowes in the plumbing department. Select oring smaller than groove so that it will fit snug and should be about 1/8 in thickness. There is a smaller oring behind piston, just make sure it not cracked and check for upper seal in head to be in place. Finally check that surface there oring seals on head is not scratched. Remove fine scratches with #400 grit paper.

sounds like a shaft seal leak..... cut power to pump ... unbolt the motor at the seal plate and pull motor from pump... take electrical cover off back of pump and hold the shaft at the middle (may have to do some digging to find it) of the back of the pump... now youll be able to remove the impeller by spinning it counter clockwise...
make sure you dont go cheap on the seals... and make certain to replace all seals on pump
(diffuser oring, housing gasket, shaft seals, and lid gasket

Usually a Viton seal should do it.

you are describing a bad seal and bearings going bad in the motor. I would replace both.

It sounds to me that your diffuser oring needs to be replaced. This is a common problem with that pump. The oring stretches out or breaks and this will keep the pump from creating a vaccum. This is easy to check. Shut the power off to the pump. Remove 6 bolts holding the seal plate together (do not remove the bolts that mount the motor to the pump). Their will be 2 bolts at top and bottom on each side of the seal plate that have no nuts and two bolts in the middle on each side of the seal plate that have nuts. Grab the motor and pull it away from the pump. You will see a cone on the front of the assembly. Check the oring and make sure it fits snug around the cone. If not, replace the oring. This is most likely what is wrong with your pump.

It has seals there for the water pump. They need to be replaced.

Lube the seal plate oring and diffuser oring with magic lube.