EHHHH, ok, I do agree if fluid is dark/burnt with no red tint at all, pass on service without considering failure later on. Generally you going to notice burnt smell due to TCC use. As long as you dont see huge amounts of trash, actual dark fluid and see no red in the fluid service shouldnt cause much issue. If its that bad its doa/on its way out anyway.
Finding a shop that can do a flush before the filter service, this way if it kicks up any debris the filter can catch it. Honestly an ATP filt from NAPA works well, but pretty much any brand works (except FRAM, never use anything FRAM, too restrictive and cheap).
I used to get some great filter kits GKN brand. reasonable prices and good filters and gaskets.
NEVER EVER USE CORK PAN GASKETS.
AND NEVER EVER FOLLOW THE INSTRUCTIONS ON USING WHEEL BEARING GREASE TO ADHERE PAN GASKETS.
I like using black weatherstrip adhesive to fasten the gasket to the pan. One caveat is dont stick it on too fast. Change the filter seal, yes drive old one out if its a press in, use appropriate too to install new one. DO NOT REUSE THEM. I have seen transmissions start having issuessucking air cause they were not changed.
Get it all cleaned up, install new filter, clean bolts and holes. have them ready and all your sockets/tools.
THIS RECOMMENDATION IS FOR THE RUBBER/COMPOSITE GASKETS NOT GM REUSABLE ONES. THOSE GO ON DRY.
I use simple bead of adhesive, stick the gasket on and sit it on flat surface gasket down, I sit stuff on top for a few minutes. Not too long. then install, BUT if car came factory with reuseable gasket dont use stock torque specs. I prefer buying the reuseable type gaskets than you never have issues.
Also I really havent had any good results with slip fix additives. If it has a seal issue add about 4 oz of brake fluid and save for trans repair/replacement.
NOW Lubegard does make a good additive to work on shudder and stuff.