don't know on which page, because haynes carefully makes sure to make their books as difficult to navigate as possible for some reason. (1B3) But it does say it for the 124 diesel.
I knew when I came to the US that the 3000 mile oil change I kept seeing and hearing everywhere must have been implemented into the national psyche by big oil!!!
And now I know!!!
Every 6000 miles lads, save your money for something else.

They are wrong. Haynes pumps out generic repair books. They should not be used for more than a basic repair guide.

3-4K for non-synthetic and 6-8k for synthetic.

what does mercedes say?

I just ripped up and threw away my haynes manual. It's too stupid to have around. Impossible to find anything in it, no page numbers etc etc. I have 2 more that will go in the trash.

2500miles for severe operating conditions (city driving) or 5000miles and at least once a year.

The 60x engines are much more clean than the 61x. 6K miles may be fine for them, but not the 617.

the 60x is clean indeed. I sold a few of them and after an oil change that oil would stay clean quite a while.
But man, Haynes truly sucks. I got rid of all 3 I had now. (never looked anything up anyway) my god, are these people on acid when the put those junk manuals together?
try finding valve clearance on the 617. or information about electronics on the (complete crap disaster) 603 idle control. it'll take about 3 hours.

don't throw em away,the landfills are filling up instead throw em in the wood burner,at least get a little good out of em.

Yes, Haynes manuals aren't the last word in accuracy and depth of content. However in the UK, until very recently, for most models of car there hasn't been much alternative. Main dealers typically will not sell you a factory service manual.

In this context, Haynes manuals fill a gap - they allow a typical DIYer to do some basic work, and by doing so, save considerable sums of money. London main dealer rates are typically over £100 per hour now (over $200 per hour). Even paying to have a tail light bulb put in at that rate would probably cover the cost of the Haynes book.

Do I understand correctly that in the US, laws force manufacturers to make their FSMs available to anyone who wants to buy one?

The remaining anti British vitriol I can easily ignore - let me ask if US products are so good, why aren't our roads full of your cars? (Most attempts to import US cars into the UK fall flat on their nose - the most recent sad failure is Chrysler)