Leaking out the back of the pump indicates the seal has failed. They are available for about $10 but tricky to get all the plastic spacers/washers etc out. Draw diagram &/or take close up photos & notes as to sequence of disassembly.
There are only a few manufacturers of bearings (one of the bearings in my pump is also the transmission
input shaft bearing for a Chevrolet, & both pump bearings are available at auto parts
stores). They are listed by size of outer diam/thickness/shaft size & are much less expensive ($6) than from pump manufacturers.
To install the impellor coat vanes tips with silicone & insert into a hose clamp that has been adjusted to about 1/4" - 1/2" larger than the bore opening. Close clamp down to bore size & slide impellor down into the bore lining up the drive pin with the slot in the end of the shaft.
Bearings can be pressed out/in of the case with the help of proper size sockets and a vise. Never press on the inner bearing race
If there is a drive belt it doesn't have to be tight. The power requ'd to drive the impellor is small.
Definitely secure a new complete pump for spares.