Originally Posted by Diseasel300

The valve plate can fail from a variety of reasons. Oil starvation, moisture contamination, non-condensibles (air/water) in the system, excessive oil, old age (normal wear), etc.

If you're already opening the system, take the time to do a flush and replace all the O-rings on everything while you have it apart. You'll flush out the old oil and any contaminants and start with a clean system with a known quantity of oil. The compressor will come charged with PAG46 oil, you can drain it and refill with the oil of your choice.

You will want to replace the filter/dryer as well. Make it the very last part you install before pulling a vacuum and charging.