I've a 1994 GT Vantara, with a steel frame. I'm not 100% sure on the exact steel type however; looking up the model and year, it could either be full cromo or just have a cromo main triangle. Regardless, this didn't prevent it from forming a crack at a welding seam, at the point where the top tube and seat tube meet. The top tube is oversized and so the seat tube was fitted through it and welded it place.
My question is: do I need to worry about it? It is only a localized crack, and doesn't seem to be growing. If I do infact need to worry about it, should it be taken in to a repair shop as soon as possible, or can I finish up the riding season and send the frame in for reapairs during winter? Thanks for any help.

Here are some picture of the bicycle and the crack




PS. sorry if the pictures are huge, no idea how to resize