Chrysler Repair: 99 Sebring EGR fails quickly: 2.5L V-6, egr valve, cylinder misfire

Question
I am having a lot of trouble with my daughters 99 Sebring - 2.5L. The problem started about 3 months ago with a rough idle and stalling. The only stored code was for random cylinder misfire. Since the car had about 90,000 miles the mechanic suggested that it needed a complete tune-up which he performed. Things were fine for 2 days and then the same symptoms reoccurred. This time the mechanic said it was due to a bad EGR valve and replaced the EGR valve with a new dealer supplied OEM valve. All was well for about 3 weeks and then same problem again. Another trip to the shop and believe it or not the new EGR had failed. Absolutely no underlying cause could be found and the mechanic attributed it to just plain bad luck in getting a bad valve. Another new valve was installed and about 3 weeks later, same problem again.
This time I brought the car to a local Car-X shop. I explained the full history of the problem and the steps that had been taken to correct it. I told them that there had to be some underlying problem that was causing these repeated valve failures and that my previous mechanic seemed unable to correctly diagnose the problem. They assured me that they would run complete diagnostics and get to the root of the problem. End result; absolutely nothing wrong, engine in great condition, all electrical and computer systems performing properly - BAD EGR VALVE! I told them that it seemed inconceivable to me that I could have had 3 brand new, OEM dealer supplied valves go bad in 2 months without something causing them to fail. There answer was to do an upper plenum cleaning just in case there was some loose carbon fouling the valves. They told me that if there was ANY other failures within 12 months or 12,000 miles they would replace the valve again for free. This was done and the car ran great; for about 3 weeks! Now they are saying that there is an internal oil consumption problem, that the EGR valve was full of oil and that this caused the most recent failure. They say that they can of course locate the cause of the internal oil leakage at additional cost and resolve the problem, otherwise, they will cease to warranty the valve. There was never any mention of oil or anything else being found in the previous 3 valves by either mechanic. I pointed this out to them and they willingly agreed that this was true. All diagnostics still come back fine, there is no indication of any oil being burned through the exhaust. I can't have my daughter driving this car when it stalls and she loses power steering. I can't keep throwing money at this with no resolution. Can you suggest anything to help me with this problem?

Answer
Hi Dan,
The '98 manual that I have discusses what the test capability of the egr via the on-board diagnostics (and resulting fault codes) and also other tests for the system's function by use of a diagnostic test tool. It could be that other parts of the egr system than the valve are causing the valve to become cruddy. The entire section is 6-pages long so it would be easier for me to xerox and postal mail them to you. If you would like the pages just use the "thank and rate" tab where there is an opportunity to comment to give me the address. Then you can ask whichever shop is seemingly reliable to look over the pages and possibly perform the additional test.
But first, I wonder if the engine is using oil to any significant extent (how many miles between the necessity to add a quart to the crankcase?). If so, then there may be an internal mishandling of the oil (leak of a gasket?). Or could the crankcase be overfilled? How about the positive crankcase ventilation valve? It is located at the front end edge of the valve cover that is labelled "2.5L..." and it is an inexpensive and easy to replace part. If that weren't working the blow-by might be causing the problem with the egr. If you check those out and it still seems to be a problem then doing the rest of the tests on the egr system covered in the manual pages would be in order.
Please let me know what you learn.
Roland