Xpantastic!

I have posted in the past about my filter FM not being consistent across all voices-2 voices in particular are always different.  Even with FM off, there are still fairly noticeable differences in the filter of those two voices compared to everything else. 

So I am assuming that either the filter chips for those two voices are going south OR the VCO chips are.  I have spares for both, but before I start pulling things out, I am wondering which chip is the more likely one to be an issue?  

Filter FM is linked to osc 1, so if there are issues with that VCO chip, it will sound off (even if the VCOs themselves are perfectly in tune).  But given that the filter sounds more bright or "different" on those same voices, even with FM off, I am thinking it is  more likely a filter chip issue...  The FM doesn't bother me so much, but having slightly different filter "openness" on 2 voices does.  

What should my plan of attack be (i.e. start swapping chips, or throw in replacements)?

Also, will I notice much difference compared to the remaining voices if I replace one or 2 filter chips?  i.e. is it better to replace all 6 for a consistent sound, or does it make any difference?  3372s are fairly cheap now, so I wonder if it is better to buy a "matched" set?