Q: Ball joint boots are cracked.

I have just had a regular service done on my truck by an independent mechanic (in business many years) that included numerous items being inspected. I was told that the ball joint boots are cracked (the lower ones apparently cracked open), and that there is, therefore, risk of grease coming out and ultimately the wheel coming off. I was told that the only way to fix the problem is major replacement work that costs hundreds of dollars. However, (as a chemist) I do not find it plausible that something which is apparently rubber cannot simply be sealed with rubber adhesive or some other liquid sealant - and, if nothing else, slow down the process of grease escaping/ dirt getting in. I do not find the advice I got from the mechanic to just leave it and periodically check whether play has developed in the ball joint before doing anything to be sensible. Is there ANY history in the car mechanic industry of doing something about this kind of problem other than leave it or expensively replace?

My car has 186600 miles.
My car has an automatic transmission.