MS 5977A baseline drops in series over 2 weeks (offset pattern)

After most MSD maintenance (filament change/switch, source cleaning, etc...) I seem to have an issue with the baseline dropping in series (offset pattern) for up to 2 weeks afterwards.  I'm new to this machine, but I'm in the process of slowly changing out parts in this 5 year old GC-MS (7890B - 5977A) that has been neglected.  I'm wondering if there is a part that I should focus on next to get rid of this annoying problem.  Every second run needs a new calibration due to failing BTEX standards (read by the MSD portion)

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