And engine oil and oil filter change are NOT part of the front crankshaft seal replacement labor operation--they're extra.
When you checked the oil and found the "debris" on the dipstick, whether such items are "hard" or "soft" can determine where they came from and what they might be. Disintegrating gasket parts, of which there should not have been many, considering where the only gasket is in that situation, will usually be larger than what you have described OR would come up on the dipstick. It's probably engine deposits from the front cover breaking loose from the engine block, which should be generally "soft" rather than otherwise. If you press them between your fingers, they should smush out.
As for the other unapproved services he performed, your local municipality should have some laws about "unapproved repair work" being performed. In some towns, the shop can go 10% over on the actual cost of the repair work, from the prior estimate, before approval is needed to do further work. IF they don't get the approval, the customer is not liable to pay for the additional charges.
Naturally, in your case, you didn't have time to press the issue, with no paper estimate being offered, just verbal, so you paid and felt fortunate to be through with that deal that day. Still, though, you might check with the municipality the shop is located in to verify any further course of action you might have.
Might it be possible that this whole oil leak issue might have been because the crankcase was too full to begin with, and especially afterward?
Generally, it's better to look for an oil leak on an overhead lift. Where it drips from might not really be where it's coming from. Usually, though, wet oil on the engine comes from somewhere and where that trail might originate would not be revealed by the cardboard method. Similarly, though, there should have been oil drops on the concrete or other surface where the vehicle was parked--the cardboard just made it easier for you to see.
It looks like your normal mechanic was trying to do you a favor for recommending another mechanic "on the cheap",but "cheap" is not always better . . . in the long run.
In general, the more substantial the repair shop is, the greater recourse you might have in getting poor repairs fixed. Most will not take jobs they can't do or don't have people trained/experienced to do them. Smaller private shops can just as easily tell you to get lost, but chains or dealerships can't do that nearly as easily if a repair has been poorly done.
ALSO, with all due respect, a used car dealer's used car mechanic is probably going to be more experienced in "flat-rating" repairs than taking a little extra time to do them "as specified". If it's a smaller dealership, there probably can be more "patching" being done rather than "fixing", many times.
On many of the front and rear crankshaft seals, there can be some "knurling" on the inner surface of the seal to help deflect oil back into the motor before the actual lip on the seal would come into play. If the seal is put in backward (usually can't be done as it looks wrong compared to how the old one was installed), then oil leaks can happen. But it might be "cocked" rather than "square".
End result, you'd better find somebody else at a reputable shop . . . even IF they might be more expensive . . . to get you a written estimate of what it'll take to get your vehicle repaired so it acts correctly and doesn't leak oil. THEN use that estimate should you go to small claims court as your "real damages". If you had to rent a vehicle to get around while your vehicle was under repair, bring those receipts too! You might also be able to get a reasonable "pain and suffering"-type of award for the time you didn't have your vehicle. Unfortunately, the total amount might exceed what some small claims courts might have jurisdiction over.
When a mechanic charges you for looking at a vehicle, that's called "check out time" and is a valid charge. Usually, if they repair the vehicle, that charge is waived. Still, their time is valuable and is worth something, even if they might be a shyster.
I concur with Putney that the transmission issue might not have been a "replacement" issue, but it could have been. No way to know that, now, though.
Regards,
C-BODY