Hi Leo
I'll try to answer your question.
Here's a photo of an impact driver, you insert screw driver bits or socket and then hit it with a ball peen hammer like a chisel. When hit the bit rotates slightly to loosen or tighten the fitting. If used on a screw it forces the bit into the slot so it won't slip easily. At the bottom of the picture you can see a couple of bits that have been twisted while removing screws, the screws weren't damaged.
The next picture is the driver in use.
As far as gaskets and seals go I would replace all of them. So far I have only shown the seal for the float valve and the bowl drain and the seal on the GAV but there is also the main gasket you mention and a couple of other seals.
Here is a simplified schematic of the fuel passages covered so far, it's a little rough but I will add to it as we go along.
I hope this answers your questions.
Jeff