I would use epoxy as it will not stick to you, or anything, for several minutes. Clean the area well with a de-greaser that will evaporate like acetone or mineral spirits, use a q-tip soaked in the stuff and squeeze it down hard into the joint as you want it to be free of oils that will prevent adhesion, then set it aside for twenty minutes or so to allow evaporation to occur fully (happens quickly in open air but takes longer in tight places). In the meantime, mix up a tiny amount of JB Weld or other epoxy. If you're talking about an extremely small gap, you might want to mix in a tiny amount of acetone to thin the epoxy; this weakens it a bit in terms of adhesive strength, but shouldn't adversely affect it as a weather seal. Apply with a toothpick or your finger and keep pushing it toward and into the gap. It WILL get on the guard and blade, but you can clean it up easily. When the gap seems to be not taking any more (remember to keep the point of the knife up so it doesn't flow out) take a paper towel and start cleaning things up. Once most is clean, switch to water dampened paper towels. Your finger doesn't have any hope of getting the epoxy out of the gap (unless it's just a huge gap) so dig in and get everything you can off of all exterior surfaces. Leave it pointed up for a few hours and you're sealed.
I would stay away from any of the two or five minute epoxies, they set up two damned fast to work with easily and their joints seem to break down after just a few years. If you want something less opaque than JB, Walmart still has some thirty minute epoxies from Devcon, I think.
Anyway, you will end up with a very clean looking fill that will seal and last much longer than a superglue fill.
