Soooo, what's the best fix for the red paint problem?

Looking at your photos, the first and third just show stone chipping, with the white undercoat showing through. This is very similar to what I have seen with red Alfa Romeo sports cars. The second picture shows the clearcoat coming away is and is possibly the problem except that if this is a plastic panel, the well-known paint problem is said to only occur on the metal panels.
My SLK is a late 2015 and appeared perfect when I examined it at the dealers in October 2020, only for what looked like microblistering to appear in late November. At the time I thought I'd get it sorted in the spring of 2021, only for it to disappear from view in the spring !! I did a small repair on the rear wing top behind the driver door where the clear coat was peeling slightly. I flatted off the clear coat all around and used an aerosol can of clearcoat to recover the area, then polished. This has held up so far. As far as I can ascertain, the fault lies in the clearcoat, not the base coat.

If you're not a rich man, then it is possible to respray small areas using aerosol cans, the trick is to use quite fine flatting paper and not go at it like a bull at a gate. My final flat paper was 1500 grade. The lower front valance needs totally flatting down and refinishing to get rid of the chipping. Not difficult, but you need warm weather. Then try to cover with some of that clear vinyl film one can buy.

When I had an aluminium XJ6 I had to do quite a lot of paint repairs where the dreaded aluminium corrosion had occurred.

I came across a brilliant Mars red SLK250 CDI with no flaws whatsoever. But considerable trawling of this forum and the others found that red paint is a disaster waiting to happen so I kept looking.

Some say it is the clearcoat. Others say it is the red base coat and the only solution is a bare metal respray. Some postings suggest even a bare metal paint job does not do the trick - that they had it redone by Mercedes and later it failed again. Some threads report the micro-blisters occur within an hour, on a cooler day, parked outside. Some say it depends on your location - that more extreme weather conditions cause it, which unfortunately includes the Raleigh NC region. MB-USA settled a lawsuit on the matter.

This morning a new posting popped up on the primary place cars are sold in New Zealand. 2011 Mercedes-Benz SLK 200 NZ New + new paint | Trade Me Motors. As you can see, the asking price includes a $7,000 fresh paint job. It will be interesting to see if there is a market for a repainted Mercedes.

I would suggest using a lot of Google searches to read the many experiences and observations as to the cause and fix. Some suggest having the peeling repaired and then vinyl wrap the whole car (but repair first or the underlying imperfections will show through).

As for stone chips, find a friendly dealer and ask them who the best paint detailer is nearby. A good detailer will airbrush the chips so they are almost impossible to see... and you are talking in the hundreds not thousands of dollars if you can get the guy who does dozens of dealer cars every week.

I'm not sure I agree with the rattle can DIY fix. If you are on a budget and want just to fix the imperfections, better to find a professional willing to do a cash job who will tell you how to prepare it for him. You do the sanding according to his instructions, remove the stuff that is not to be painted and carefully tape the stuff you can't get off. You buy and supply the paint to his specs. Let him do the spraying. It's an art learned with years of experience. But don't just fix what has failed. Do your homework to research where it may fail in the future.

Sorry coming so late to the discussion. My wife's 2012 SLK200 had micro blistering start to appear about 18 months ago. a guy at work had an immaculate 2012 red C-Class so I asked him if he had any problems. He told he'd had it resprayed previous year under warranty and to visit my local MB dealer. I phoned them and they asked me to book an appointment with their bodyshop. I went down and they had a look at it. I was expecting all sorts of excuses against doing anything with a 9 year old car, out of warranty etc. etc. but no. The bodyshop manager agreed there was micro blistering going on and as it was a known fault MB were doing a full respray under their warranty. He told me MB were covering the cost for up until cars reached 10 years old. They even gave me a courtesy car of a Mini Cooper for a week whilst it was in. MB don't advertise it but they will stand over it. The bodyshop manager told me he had about 8 red cars in for same problem. The only parts they do not respray are any panels that have already been resprayed. A quick check with a paint thickness meter identified those, in my case the roof and bonnett. But I was more than pleased with the result.