I just did this a few weeks ago on my car, resealed the breather covers and replaced the valve cover gaskets. It is tight and I did remover the fuel line. So far I have had no issues with leaks. My valve cover gaskets were not leaking but once I had the covers off i noticed that the rubber was hardening in some places on the gaskets, so I am glad i did both even though only the breathers were leaking. I also would advise that if you are resealing the breathers taking the entire valve cover off first insures that you do not drop any pieces of silicone into the engine. Its more work but also a safety margin. I spent an entire day removing cleaning and replacing the valve covers on the car, but I took my time and it seems that it was worth it. I personally prefer to take my time and (hopefully) not have to make the same repair twice.

Good Luck!