Just to add my two cents worth, I agree that 420 is the solution. It will go to the bottom of any crack that is open to receive it. But, I had a tip crack UNDER the finish once and have had to fix similar cracks in risers and limbs. If the crack doesn't come through the finish-test with your fingernail-then I'd advise sanding the finish off in that area and refinishing after the 420 dries. A tip is very easy to do. Often you can carefully dip it in a small container of thinned finish and let it drip dry. Use several dips.
The other method to open the crack to receive the 420 is to take a sturdy pin and carefully scratch along the trace of the crack. Get clear through the finish so you are certain the crack is open. Apply a tape barrier as close to the crack as you can. Then take a hypodermic needle and suck up a little 420. push the plunger to get a tiny drop on the tip and then back the plunger off ever so slightly so the needle tip just appears wet. Then use it like a pen to trace the crack. The "ditch" you scratched in the finish-along with the tape barrier should prevent the 420 from flowing all over. Apply several coats to insure the crack is full. When it dries sand(1500 and then 2000 grit wet/dry paper) and polish to match the surrounding area.
I make custom sanding blocks for small repairs by gluing a dot of 1000, 1500, and 2000 grit to the eraser of a new wooden pencil. Write the grit on the side of the pencil....it will last for several repairs.
Above all, don't just apply 420 to a surface where you can't control it.....it is thinner than water and WILL make a mess! (but it can be sanded off w/o much problem.)