800 flow control oil leak

The flow control on my tractor has leaked oil for 30 years. I have replaced the o rings a few time but can't seem to stop the leak. Is there a secret handshake, witch craft, or some special o rings I'm not using? It's a vane style pump on a 1955.

Can you tell if its coming fron the inside of the oring or the outside of the oring? Clean it with starting fluid and stick the corner of a paper napkin to the area you want to check. Try this place. Marco Rubber
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Square-Profile Oil-Resistant Buna-N O-Ring
1/8 Fractional Width, Dash Number 216
Packs of 50
In stock
$8.18 per pack of 50
4061T238
Material Buna-N Rubber
Cross Section Shape Square
Dash Number 216
Fractional
Width 1/8
ID 1 1/8
OD 1 3/8
Actual
Width 0.139"
ID 1.109"
OD 1.387"
Hardness Durometer 70A (Medium)
For Use With Grease
Hydraulic Oils
Specifications Met ASTM D2000, SAE AS568, SAE J200
Temperature Range -30? to 212? F
Color Black

I can't tell exactly where the oil is coming from. Should I be using square profile rings instead of round? There were round rings installed when I took the flow control off the pump originally so that is what I put back.

The parts book calls for a -011 70 duro. I don't really care for hardware/auto parts orings. Since I work on hyd cyls almost day and we buy seals sometimes by the hundreds a day there seems to be a big difference in quality. I would go to your local hyd repair shop. They buy from the previously mentioned places and other companys that specialize in hyds.

Thanks.
hopefully the advise from riveroadrat and yourself will solve my issue. I've probably been using the wrong o ring all this time.

You need to find where your leak is first to fix the problem.