Well it's all been said really, but yes, rust is a fact of life with an old car, kept outside. I have been attacking rust on my 2004 TF for years now. Four of the eight subframe mounts replaced, both front suspension wishbones, both subframes derusted 'in situ' and treated and sealed, various paint chips treated especially on the bonnet and around the lights, also rust starting on seams at the top of the windscreen frame (take off the rubber seal to look), also under the rubber boot seal, also in the gutter behind the rear window, not to mention all the steel bolts in the bonnet area and the slam panel for the bonnet catch, plus the rusty bonnet catch security pressing underneath the slam panel. Then of course there are the wheel arches, rust always starts on the inside of them where the arch forms a sharp edge and tries to work its way out to the more visible areas. My latest fix was one of the sills, which had surface rust bubbles and tin-worm tracks aplenty. It's a lot of work - a lot. I do it all myself. There are two ways to go at it essentially - the wire brush over the offending area and a quick spray with stonechip or whatever, then the OCD approach - I do the wire brush bit then burn off every last bit of rust with builder's acid (careful) then treat with the rust treatment phospate/phosphoric acid solutions which are less brutal than builder's acid but take a long time to work if there's pitted rust - but they do leave a protective film which gives you a short time to spray the area.
I also do rust prevention - flood the sills with Dinitrol cavity wax, also any hollow structural member (pick a dry week). Put a cover on in winter (at least one that covers the hood and windows).
I think it all comes down to whether you want to have carefree motoring with just a bit of an oil change once in a while or want a challenge :0) These cars are of course now 15-24 years old and I don't think it's possible to have a car that old, built at Longbridge, and expect them to just go on forever without major work at some point. I ought to say I have 'preservation' of my TF in mind - for some time to come - so am OK with the level of faff involved in keeping it working and the rust under control.
