[Espeefan]

The gauge most likely was a liquid filled gauge. They fill them with liquid to reduce the pulsatation effects of pumping and help dampen the needle movement under natural vibration and pressure spikes. This is probably why you see the needle jumping all over now. Sounds like the gauge leaked out it's liquid, which is not hyrdaulic oil, by the way, but usually a glycerine, silicone, or halocarbon fluid.

If things were running fine before you tipped the machine, then perhaps the tipping caused the pump to suck in some air, as the oil level might have sloshed forward or away from the pick-up. How does the model run now? Are the cylinders jumpy and jerky? That would be air in the system, which I would think should eventually bleed itself out, after a few cycles. Unless your pump is not self-priming, and I don't know if it is or not, it could still have air inside it, or the system, causing problems. In that case, maybe try priming the pump by filling it's case with oil, before starting it up again. Once it starts pumping oil, any air in the system should be worked out in a short order, as the cylinders and valves are cycled.

If you feel the need to bleed the air out faster, then you might have to loosen a cylinder hose fitting (on the cylinder that acts soft, jumpy, or jerky) a small amount, cycle the cylinder, and watch to see if any oil seeps out of the loose fitting. You can do cylinder both ports, but do one at a time, and do the end of the cylinder that is being pressurized. Tighten it back up, once you deadhead the piston, and before you switch directions to do the other port. It might get a little messy, so be ready with a rag to collect the oil.

This is usually what I do at work, if I have air in a hyrdaulic system, but the majority of the time, the air will work it's way out on it's own, when the oil returns to the tank.