CPAP machine seems to not put out as much pressure.

I bought a cpap machine used off someone, it's a REMstar w/o cflex. I've changed the settings on the device to various pressures to test them. When I first got the machine anything above 10 seemed difficult to breath against, but over time the pressure from the machine didn't seem to "push" as much. Currently I have it set to 18 with a ramp of 12, and it doesn't even feel like it's on when I wear my full face mask. There's pressure, enough to slightly blow my cheeks out if I open my mouth, but nothing like it was when I first got it. Also, if I set it up to the max 20 it will run for a few seconds then shut off, the LCD will flash off and on and then it will start again and do the same thing, run for a few seconds then shut off. I opened up the machine to look at the components and it seems that I wasn't the first one to do so. The clips on the fan casing seem to have been mostly broken off, and it looks like the fan blade was loose on the spindle and actually made contact with with the casing at one point as it has some shear marks in it. I'm concerned that it might have damaged the fan's motor making it not able to achieve normal speeds. I pushed the fan back down on the spindle and used epoxy to secure it down so it doesn't come in contact with the casing anymore but it still doesn't seem to put out what I think is decent pressure. Having no way to measure it I don't really know. Has anyone else had similar experiences where the machine doesn't seem to put out decent pressure regardless of setting? Obviously the higher up I go, the more pressure it puts out, but it doesn't seem like it's the "right" pressure for that number based on what it ran when I first got it. The shutting off at 20 thing seems to be a related issue, but I don't know.

When you first start on CPAP the pressure seems unbearable, but, once you have been on it for a while it seems very mild.
You can take your unit to a DME and they can test it for you. It takes just a few minutes. There are ways to test it yourself if you are handy. Someone will come up with the instructions. I think you are just getting used to the CPAP. I would NOT continue to increase pressure unless you are sure that you really need it to prevent apneas. All CPAPs have a maximum pressure of 20.