OM great info, thank you

Well it's been a Saga. Replaced the main suction hose that goes down to the trans pickup, and 2 solid hose clamps. Hose was fine but found some damage on one of the elbow fittings where somebody had cut a hose off with a grinder and thought we had it. patched that up but no good.

Replaced the other hose that goes to the lubrication circuit as it was made up with field fittings. no difference.

Replaced more O-Rings, started looking at steering and clutch circuit in case that was causing the aeration and that was the cause of our low pressure on the trans side.

Then the pony starter wouldn't turn over so had to order new brushes for that.

Started planning on sucking all the trans oil out and doing the 2 O-rings at the back where the pickup goes into the oil drain/bevel case. Pasted the joins with silicone in the meanwhile as there is about $1000 worth of oil in there.

Then on Sunday afternoon i was around drinking beer at a mate's place and another bloke who was there reckons he had a blocked breather in his backhoe that caused all sorts of weird problems.

Went out, removed the breather that sits under the fuel tank on the bevel gear case and it's very blocked. Fired it up and and went for a bit of forwards action, it spluttered a bit (i guess as it bled the air out) , then smoothed out and off she went.