Technical Hydraulic Question on Main Pump

Got an old Clark/Bobcat 443.

The auxiliary gear pump went and the only replacement was a "kit" for $2500.

I found an off the shelf pump with the same mounting configuration and displacement for 1/10th of the price $250.

Now, one thing I noticed about the old broken pump was that it had one or two tiny holes in the housing near the drive shaft. On the main swash plate pump side, the chamber where the drive coupling is housed also has a hole but a bigger one. When the auxilary pump mounts to the main swash plate pump, it seals with an O-ring, and this coupling housing fills with oil. I know this because when I first removed the aux pump, a load of oil drains out from the coupling housing.

The new aux gear pump does not have any tiny holes in its body, but I have no idea if that is a big deal or not.

Anyway, I don't know if this is coincidence, but now I have oil pouring out from a completely different place. Where the vertical control shaft (the one operated by the control handles) enters the swash plate pump at the top, oil is oozing out at quite a rate.

I have no idea if this is complete coincidence or it's connected with the new aux gear pump not having those tiny holes in its housing.

Sounds like you will need to add an external drain for the hydrostatic pumps

Are the pumps enclosed in the chain case on that model, so any oil that leaks out of the pumps just drops back into the oil sump? Or are the pumps setting out in the air? Dating myself but the ones I worked on back when everything was inside the center case under a gasketed cover.

Thanks guys.

Each side (left/right) is a closed loop circuit. Wheel motors are in the chaincase, and swash plate drive pumps are under the seat (in the air). The aux gear pump creates a charge pressure in these 2 closed loop circuits.

According to the hydraulic schematic the swash plate motor housings are filled with oil at case DRAIN "pressure" (basically nothing, just tank pressure). The coupling housing is also at that tank pressure.

I'm starting to guess the tiny hole in the original gear pump went to its suction side, and without it the swash pump housings are building up to charge pressure. Maybe what's needed is a tiny drain hole in the top of the coupling housing and route that to the tank. Come to think of it without any means of oil circulating in this coupling housing, the splined coupling will not get a replenished supply of lubricating oil.

Edit:

Just been and dissected the old knackered aux pump. There are 3 small holes right next to the input shaft:

Hole 1 - goes to one of the bronze bushings (gear shaft), no doubt as a means of continuous lubrication.
Hole 2 - goes behind the pressure plate on the low pressure side (suction)
Hole 3 - goes behind the pressure plate on the high pressure side BUT there is a one way ball valve in the housing too. So when
pump high side pressure is more than the pressure in the coupling housing (i.e. outside the pump) this ball valve is forced
shut.

So in a nutshell, the old pump was continuously sucking oil from the coupling housing, while case oil from the main pumps was filling the coupling housing. The new gear pump is just a "dead end", and allows the pressure to build up in the main pump case.

Just something for anyone to note if they put an off the shelf part on.