All 105 set up older components (>10yrs). Triple 10 speed, 52/42/30, I think 5510 shifters (shifter cable comes out the side).

The FD is a clamp on. It is rusting and paint is bubbling underneath it. The mounting screw is totally corroded and the allen head it stripped. I could just replace the screw, but I think I should replace the whole unit. I'm looking at the 5703 but I'm getting conflicting info about the large chainring. Shimano says up to 50T, but I've read elsewhere it will work on a 52, which kind of makes sense to me.

I'd like to hear it from someone in the know.

Also, would an Ultegra SL 6603 work with my setup? If so, I've only been able to find it as a braze on. Does that make it a "no go"due to the expense?

Thx I'm trying to do this all myself haven't talked to anyone at a shop yet.

If the FD is working, then I wouldn't replace it, I would do the bolt as you suggested.

I think the 5703 would work if you go that route. The specs say 20 teeth difference but there is always a little leeway.

For the 6603, if you can't find a clamp on, you could always buy the braze on clamp and attach the derailleur that way.

Good luck.