I need an O ring... what else could be wrong as I can get no pressure

The valve-o-rings + [ parbaks seals ] where the pressure can be adjusted with.
Control the water inlet filter or hose that there are no waterlock couplers are used or is mounted
on the wrong site on the hose , that it is used as water inlet on the tap.

Also, could be a broken piston ring, if oil continues to come out after clean up and running for a few minutes, you will need to do a dry then a wet compression test, if there is no difference in the pressure from wet to dry, then it's valve related, if there is difference, it's the rings.

You are probably missing the washer or O-ring. Loosen and separate then check. It may also be a broken O-ring.

A few reasons would be a problem.
Check O-rings in the fittings
Check all air connections, one-by-one with soapy water for bulbs - fix as needed.
Check a pressure switch - it is often a major problem
Or even better to replace with Digital Controller.
Check this site: www.CompressorController.com

1. First, you will need to depressurize your fuel system. Remove the Fuel Pump Relay, start the vehicle and run until it shuts off, should only take a few seconds.
2. The Fuel Pressure Regulator is held in place on the Fuel Rail using a Retaining Ring, or Snap Ring.
3. You will need to remove the Vacuum Hose connected to the Fuel Pressure Regulator before you remove the retaining ring.
4. You need a pair of Snap Ring Pliers to remove this retaining ring.
5. Once the retaining ring is removed, slide the old Fuel Pressure Regulator out, and install the new one. Lubricate the O rings on the new part and the fuel line before assembly.
6. After reinserting the Snap Ring, ensure that it is snapped in place completely.
7. Reinstall the Vacuum hose and reconnect your Fuel Pump Relay. Turn the Ignition to On, and check for leaks around the Fuel Pressure Regulator.
8. If no leaks are found, proceed to start the vehicle.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

More than likely you aren't doing anything wrong, try putting some grease on the o-ring inside of the quick connect socket and push the nozzle and wand against the ground and slide the brass ring down. If this still doesn't work I would recommend replacing the quick connect socket with a new one.

You purchased the wrong o-rings, the o-rings that you purchased are for the hose ends. Karcher doesn't offer the o-rings for this valve but do offer a replacement unloader valve. See attached link to read more about the revised valve or to purchase

Usual cause is the pressure valve sticks closed and doesn't admit more water to be pumped. Usually needs new O RIngs and cleaning the bore... ABout a 15 minute job at most. Get an O Ring kit for it.

The valve is held shut when pressure on the output is high. When you open the trigger, the pressure drops and the valve opens letting more water come in from your garden hose.

The O RIngs dry out and bore gets dirty. Polish it with crocus cloth on a dowel rod. Lube the O Rings with lube intended for O RIngs.

You need to look at the pressure regulator and the little hose going to it! It is usually located somewhere on the fuel rail!Good luck!

Diagram here
It could be the Overpressure valve is leaking #20
It could be one of the small valves is not sealing #14 and #15
The soap valve could be not sealing #7
I have also seen micro cracks in the cylinder head #8
Good Luck