Disco 2 Discovery 2 air suspension compressor blowing to exhaust line

I was driving when air suspension warning light illuminated in the instrument panel. The car wasn't sitting down but I'm able to see that it is not filling the bags currently. Air compressor is running nicely and it will turn on when rising button has been pressed on dash. When the compressor is running it is blowing to compressor assy exhaust line and I'm able to feel lots of air coming from exhaust line, not to bags as it should. On last summer it was doing similar things and the issue was resolved at garage by blowing pressured air into exhaust line and suddenly it stopped blowing air to exhaust line when compressor was running. Now I've tried same thing at home garage without no luck, it just continues blowing to exhaust line. What could cause this problem, is there some stucking valve in compressor assy itself or somewhere else? How about WD40, has anyone tried to spray WD40 to comressor intake line, would it help or will it cause other problems to system?

These kind of botch with WD40 or compessed air would not fix it , there is a pressure limiting valve on the output which can be stuck open and let air out, the exhaust valve stuck open or the air supply valve stuck closed, investigation is needed... or a new assy