Looking at the picture it appears to be beyond repair. You may need to start again with new ones (is it one or a pair) and keep them clean with non abrasive cleaners.
I don't have this problem for now as I have as you said "hidden" exhausts.
In my pre-mercedes days I had a Lexus for weekends and a Citroen Volcane to rack up the mileage and weekly (820 mile) motorway commute. I added a stainles steel back box (along with 16 inch rims) for the sound and aesthetics and polished it every 2 days with wet tissue after re-fuelling. It always gleamed in the sun before another v.quick blast up the motorway. Never knew a "square" old volcane could be so enjoyable. Commuting fun.
Well.... I've had a quote of £98 each to replace the exhuast trims
However the warranty guy says that they may well be covered and I will get to know this sometime in the next....decade?
Don't hold your breath!
...But he's just phoned back and said they will get some in for me and fit them in a couple of days!!
Result!
New exhausts tips are now on the ML and they are spangley and clean with just the hint of a wipe
Never used the warranty system for a cosmetic issue before, but great service and no questions asked.
Note to self: You can't polish a Richard the third!
Shiny sinks is superb, I found out about it from another thread on this forum and it brings all my chrome up like new.....and the wife says it brings the sink up lovely too!
Good result Mactech. I had a warranty claim on the driver's side leather seat on my CLK. Spoke the stealership on a routine visit and mentioned slight fray on the driver's seat bolster. I said I was unhappy as the car had only done 35000 miles. The service manager called out the "warranty manager". He examined the "wear" and ordered a new seat cover. I was as pleased as punch. The nearest I came to that was Lexus after 3 year's ownership and the car was 2 months out of warranty. They ordered me 4 new alloys..ok they were Lexus UK refurbished but they looked like new and I was happy.
I use autosol and it's done a great job for me. When I bought my car at 3 years old it looked like the exhaust tip had never been cleaned. I took it off the car and a good amount of elbow grease later and it looked almost like new.
I once used wonderwheels on a previous cars chrome exhaust and it dulled the finish.