So I (like most sIII's) have rust that has come up from underneath the windscreen and the rear window as well. I have removed both and grinded them down to bare metal. I do have a couple spots where it has rusted all the way through. The holes are too small to put a metal plate in to weld it up.

I am also on a bit of a budget, however I dont want a budget fix that will haunt me later. So would bondo be sufficient or is there a way to have it spot welded? I cant afford to have it leaded otherwise that would have been option #1. Any advice would be great!!

 

just make sure the bare metal is treated. Then you can bondo, fiberglass, etc.
Of course metal is preferred, but with such a small area just about any repair will suffice.
There are MANY metal bonding adhesives so that you do not need to weld. You can check those out before paying someone to weld.

 

Depends on how far away....later; is. If you don't cut it out and replace with metal, even with a much larger section than you think it needs. The rust will eventually return.

Pity that you don't show a pic or two.

 

You can also fill the holes and pitting with body lead, if you get the metal clean enough. Series 3 cars already have lots of lead in them. It is longer lasting than plastic fillers, as it is chemically bonded to the steel.

 

Im on vacation right now, but I return tomorrow so I will post pics as soon as possible. I have treated the rust with a chemical rust solution which is supposed to prevent the rust from spreading.

 

The only way to prevent rust from spreading is to CUT IT OUT. Then you seal the fresh metal, even then over time it will rust.
No 2 ways around it. Once you get rid of the rust use the best sealer primer you can find.

 

Rust is one thing but how do you prevent water from 1. entering the engne bay and 2. puddling in the area that the wiper motor sits? I have tried to find a drain hole I can unblock but ended up drilling a hole to make sure it drains. Not the best solution to drill holes in a rust-prone car. Any answers please?