I'm looking for advice on buying a used one of these. Budget is $25 to $35k and preferably a petrol model. Are there known problems to look out for and high maintenance items and what are annual service costs like?

Apparently they are one of the preferred cars of drug dealers, so most costs will be an arm and a leg, or even a kneecap.

So I'm looking for an automatic model?

It depends on how few limbs you need I suppose. Remember to check the glove box.

I6 would be preferable to a V8. Check if gear shifts are smooth in all driving conditions, ESP under heavy load (not suggesting to load it up, but try accelerating hard going uphill) if there is a jerk, it could mean a gearbox issue, or (worse) the dual-mass balancer is on its way out. Bad news, 1000s of dollars in parts alone. Bimmers use ATF for power steering fluid, if it covers(seeps through) the hoses, no way to get rid of it, everything under the hood in that area gets covered in sticky shite. Does not make it drive any different, but looks nasty and helps knock off a few dollars. Sway bar links are weakest part in suspenion, but they are the cheapest too. parts are generally a murder, anything to do with electrics especially, so have a profi give it a look see and drive it around to see what's what.

sorry, forgot to mention that.

CV boots deteriorating quickly are a common problem and $800 to get them replaced. If they are not replaced the joints will go.
I had a 3.0 I Sport for 3 years, great car

Convinced now?

Iirc the sheet metal is either zink-plated steel or aluminum, depending on the year, e60 5er front end is defo light alloys, can't be sure about the x series though. Anyway - none of that rusts, if you see ANY signs of rust, it might be an indication if a botched repair. All the way up to installing a cheap Chinese knockoff panels and painting them with the wall roller.

Check for the kids when you're reversing ...

Will the 6 have enough power considering the weight? Is RAC worth a go for a pre-purchase check?

I think they have reversing camera tech.

That's handy if you can't see out of the Ego Tank naturally.

All the same, you may want to take a look at that screen before you use a body as a speed bump.

It's fine with the 6, best engine ever. V8 has more oomph obviously, but IMO not worth the trouble.

You'll attract the wrong sort of attention in it.