Cleaning the chrome on a leica

Zippo fluid first.
Faucet water if you must... But any ingress is bad.
Don't clean the optics.

diluted vinegar on an ear swab, clean water afterwards.

I was told furniture polish (that is, the traditional bottled liquid ones, not the sprays that are common nowadays, and in the clear flavor, not the dark one). It works surprisingly well. It will clean off dirt very easily and restore the natural shine of dull chrome without making it look unnaturally "greasy". Of course it cannot repair scratches or abrasion.

In 1904 a German chemist formulated BALLISTOL oil on the demand of the army.
When I was shooting with Leica (M5), I used it to keep the leatherette in good shape and it made the chrome 'shining' too.
Now I use it on my Hasselblad, and the dove tails on the Linhof Kardan GT .

This gun oil is meant for everting: a soldier might need it in the field for gun-, uniform-, shoe- maintenance, corporal (little wounds) care and animal care.
Horsemen use it to take care of the horse's hoofs and the skin when irritated by the head-collar, hunters to heel their dogs when wounded in the bush, fishermen for protecting the winding mechanics of their fishing rods against the moister, bikers on the rubber handels, sailers for the pulleys, photographers for their (antique) wooden camera's and bellows.
You can use it safely for what ever you can imagine...
You can drink it (a little sip) when digesting is causing troubles... There is a "Ballistol Human" version, more purified components.

BTW, Gen. Rommel lost a battle in Africa because the RAF bombed a German supply transport, amongst it a load of Ballistol, so they could not take care of their guns (sand) and, above all, sunburns...

Car wax! The best way to clean and renew appearance of Leica or any other camera’s metal surfaces, chrome or black paint, is car wax. My best friend, guru for Leica nuts worldwide, has used Turtle Wax for many decades to enhance a camera’s appearance. I would not use any liquids to clean a camera.

Yes, no liquids on the camera, not directly at least!
But some oil on a cloth (or a cotton swab) and then gently rubbing, would do no harm.
And believe me, or not, Ballistol would do no harm either.
I learned that about 30 years ago from a German camera technician who was a formal Lieca Wetzlar employee, and did it since then...
But I would not deny the use of car wax because I don't have any experience with that product on camera's.