This is a Michelin transworld city tire about 300 miles old. I've been riding on this slash for 200+ miles (that is to say, 200 miles after I found it). I commute a short distance on pavement and a tiny stretch of dirt everyday. I haven't flatted and I don't think the cut has expanded at all since I first saw it. I'm tempted to keep riding on it until I flat because of it.

Should I suck it up and buy a new tire? And if you say yes, should I trust the Michelin Transworlds again? Is this a fluke?

Last thing: can I put something on the inside of the tire to prevent the tube from bulging out of it, thus prolonging the life of the tire?