well its not that its a problem but in my eyes its always been easier and less headache to let the glass guys do it. they are professionals and know what theyre doing theyll do it quick and fairly cheap. They do it every day and know exactly what theyre doing. Plus as i said if theres a leak which almost never happens with a glass company, they will come fix it for free.
If you lay that bead of urethane on there and there is one minor air pocket or pinhole in it your gonna get a leak...then your gonna end up either calling a glass company to get it fixed, or pulling the whole window back out, which is no fun task. By all means go aahead and try it if u wish, I told u what it is that you need, but ive been fixing cars for yrs and have always found it easier to leave it to the glass guys.