Just Bought 97 Sierra

I just bought a 97 Sierra 1500 V8. Anything I
should look out for? Seems to run good but I
found water in the cab after a rain coming from
the back window. I'm wondering if I can seal it myself
or what. Thanks

Are you sure its from the back window and not the third brake light

Thanks Alot! That makes sense considering where I found the
water. The little "tub" behind the drivers seat was about a
quarter full. I haven't checked it out yet but seems like
something I can handle