I've never had to toy around with injectors. How can I check if they're fouled up? It that easy to test? I have the manual, I'll dive into it later and see what it says.
Yea, bad coincidence maybe. Sucks when that happens.
I'd still run her nice and hot, underway for a while, before doing exploratory surgery.
The only way I know to check your injectors is to remove them, which isn't usually all that hard. It requires removing the fuel lines first, usually from both the injector and the pump, as they should not be bent, but easily can be, so don't be tempted. There are a variety of ways they are held down to the engine block, but usually straightforward.
Pulling the injector out has one very important consideration. If your engine has sleeves around the injector, they can be holding back coolant, which you can not allow to leak into the cylinder. I've not had a raw water cooled engine, so I'm not sure if any of those have this issue. It's most wise to drain it off first, but you may also need a tool that holds the sleeve in place, while it pulls the injector out. This tool is very handy to have over a lifetime of boating, as it also helps gently extract a stuck injector. Some screw on a little slide hammer, but that's always seemed aggressive.
Once you get them out, you have a pro shop do a pop test, which confirms the spring inside is properly holding back the fuel, until sufficient pressure has accumulated. They also test the spray pattern. Many injectors can have the spring or spray tip replaced, if either are a problem. Some injectors can not and simply need to be replaced.
A quick DIY hack is to just clean up the spray tip yourself and reinstall. When they go back in, all the copper crush washers must be replaced, or they will leak. They are cheap. You also need a torque wrench and spec to know exactly how to tighten them back down. Good idea to clean up the sleeve and especially the seat, before putting them back in.
I'm just trying to answer your how-to question. Again, if she's running fine, I'd take her out and get her good and hot first and then see how she's doing.
Btw, they sell spill containment absorbant booms that you could fashion around your stern, if you're concerned about contaminating the marina. They'd draw attention too, however. They just look like tubes of the white oil absorb pad material, in a string, which float and absorb oil but not water.