...I've been told that I need to take it to an autobody place to have them repair the rust problem so the windshield can be sealed properly.
I was just checking to see if this is the correct fix...
Sure is...sealing the leaks with silicone will only buy you time against shorting out the fuse block or causing an electrical fire while the rust is still working it's magic.
Just replacing the windshield and doing nothing else is foolish. The rust will eventually bubble out and cause a crack starting at the glass's edge. With only 160K on the clock if it were me, I'd most certainly see to it that the proper route was taken and the rust was completely eliminated.
I am facing the same repair on one of my B4s...I've got actual rot pinholes and larger expanses open to the weather buried under silicone and have resigned myself once again that to be done right, I have to be the one to do it. I spoke to autobody shops a while ago when I was just dealing with straight rust and looking for media blasting to be done. One shop even said they would clean the area with a wire wheel! and paint over it. Right there I abruptly ended the conversation and we never got to the part about the money.
Not all body shops are set up for media blasting. Few are willing to do it, at least in my local area. If that is the case around you, You may have better luck approaching vintage auto restoration folks instead to get the level of craftsmanship this job requires.
Be very picky about whose windshield you use as well, stay clear of Pilkington- the fit at the corners is horrible due to out of tolerance molds purchased from higher-end aftermaket auto glass manufacturers. Go with one from the VW dealer, yes they are still available...I purchased one for $163 about 4 months back in preparation for my upcoming 'surgery'
I'll be removing the rusted sections and grafting in donor metal from another B4 pictured below that is probably 6" high as I type this with a TIG welder and a lot of patients. I've never done this before, but stubborn fleetpride demand that it be done, and done MY way. The body shop can paint it after I've finished...most are qualified to do that
Not bad for $40 plus a few other plastic interior goodies.
I've got way more donor metal than I need to cover any "surprises" and it's a lot of work I know. All because some installer-goon did not know that VW has a ripcord buried in the rubber surround that tears away the outside bond easily, quickly and with no paint damage. Even shows it in the Bentley manual. The inside bond is broke with a long reach thin handled razor.
I hope this helps. Just remember 2 things: this is one of those areas where compromising is more expensive than doing it right and ignore most of the 2nd post in this thread