If it was mine I'd replace the pump unit. They come with wiring diagrams and a reserve tank. For an example to look at go to Graingers.com and type haldex barnes in the search line. The standard units such as Graingers part# 4NE83 come with a 2 qt. reserve tank. Some come with a 3 qt. tank. Models to look at would be the 4NE18, 4NE15, 4NE16, 4NE17, 46C519, 46C520. 2 1/2 gallon tanks #4NE25 or 4NE27 are available. Check the ones that come with the remote switch as they all don't come with a switch and wiring. Maybe you could get the lower priced unit if you can re use your remote switch. If you decide to buy from another Haldex dealer Graingers lists the manufacturer model number for each pump, just write the one down you need.
If you have a hydraulics shop in your area you could drop your unit off for repairs but you may not have it back by next week.