Jay, man, where are you located? Hopefully someone local to you can lend a hand, or an ear.
How do you know you got a misfire in cyl #4? Were you using some kind of scan tool? Did the check engine light come on?
If you don't have a check engine light, and only saw a random misfire on a scanner, then there is nothing to worry about. Misfires happen all the time for various reasons, and it doesn't mean you engine is going to blow up!
If you did get a check engine light, and used a scan tool to identify the code, what codes were present? It would probably be P0300 and P0304. Even with an illuminated check engine light, that doesn't necessarily mean your engine is trashed.
If you had a flashing check engine light, then that's an issue. I'm not going to needlessly worry you, and I think you would have given that information if it had happened.
Don't get so worked up just yet! It's probably nothing. You'd KNOW if you were having a bad issue that required mechanical intervention! Hopefully that assuages your concerns a bit for now! Once I have a better idea about what happened, I can get you pointed in the right direction. If we can't get someone local to help you out, I don't mind providing help via phone/txt/whatever! As far as the catch can goes, I don't think it solves any problems. Piston issues aren't being caused by crank case blow by, so a catch can wouldn't help in the slightest. Also, don't start buying spark plugs and other parts yet until the issue is identified. You don't want to just throw money away! Any chain and most privately owned repair shops should be able to perform a compression test. It's not anything specific to Cadillac, so a dealer visit wouldn't be required.