is the end of that seal fastened down?.... if so, thats the reason that it tore.
the wipers must be free to swing in the direction that the slide is moving, and if the ends are fastened, they cant swing and will wear/tear at that spot prematurely... and in that spot, its not as critical as it would be if it were in the middle somewhere.
I dont know how to make a repair in that location hold for very long but normal tire patching will repair it, but the problem is in that spot the rubber flexes and bends in an odd way and any patch that you put on it will stiffen the area causing more stress in the same location as the slider moves in and out.
if it were mine, I would leave it as is until its seen to be a problem and allowing moisture to get in when the slider is extended. it could go for years without any issue, or you could try to repair it and possibley cause more problems than it has at the current time, which would then require a new replacement to be installed...
if its this style of wiper, which it probably is,
https://www.camperid.com/ap-product...QwfYKjVtxXBzD0vq-65KhYQiEuCG6PyUaAm2rEALw_wcB , it is very simple and quick to replace the entire piece....