stained stainless and chrome

[j3gq_imp]

All above advices are good.

Very tough maintenance as beautiful Spain is located between the Mediterranean Sea and the Atlantic Ocean, both of high salinity, 38-40 ppt and 33-37 ppt respectively.
Exhaust is getting hot and cold and salt just loves this type of catalysis.
You need more frequent chrome maintenance with adequate product to your climate, in general.
For your exhaust, I would recommend ceramic coating treatment.
Here is the link explaining what it is:

http://hightechcoatings.com/

Do your local research first. Good luck.
I think, you live close to the water line...?

When I saw your link, I opened it and went to the product page. Here is the first sentence I read:

High Tech Coatings Ceramic Header Coating is a Patented Metal filled ceramically bonded inorganic coating that is non-electrostaticly applied and cured at high temperature.

I am not saying it cannot or does not work, but this sentence does not really inspire a lot of confidence - neither in the product, nor in AI for translation.

Before anything else try rubbing it with wet aluminium foil.

Are you serious ? (not meant sarcastically)
How can metal on metal not produce scratches, even if one is soft and one is hard ?