tailing issue for one peak type

I currently run on 6890 for leachable testing and use a leachable ID solution as a retention time marker. the marker contains diethylene glycol monobutyl ether(DGBE) and diethylene glycol butyl ether acetate (DGBA) in acetonitrile. however after maybe just one run the DGBE peak will start to tail badly and get worse while DGBA will remain consistent. im assuming this is an activity problem because of hydroxyl group? I've started using a ultra inert GC column with gaurd column and an ultra inert liner but the problem will always start up again. anything else in the flow path that can cause activity issue? anything i can change to slow/stop this tailing?

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