Did search on oil, need opinion on SAE grade!

[J.HIDALGO]

It is NOT another how often question or how to do it but, what weight should I use with dino oil in Florida?.
According to the owner's manual 15w-40 and 15w-50 can be used in +5 to +86 F or 10w-40 and 10w-50 in -4 to +86F can be used year-round. 5w-20 to 20w-50 and everything in between can be used in less than -4 to more than +86 F.
Being in North Florida, temperature is pleasant year-round (I do not like cold weather) 80-90's summer to a rare 30-40's winter. I want to use the proper oil weight for my car (which has over 240,000 miles) recommended by MB but, at the same time, I know my owner's manual was printed 16 years ago and a LOT of things have changed since then, including oil recommendations.
I want to hear opinions and experiences from MB owners and MB techs in this forum. I did a search but found nothing specific.
Background: I'd been using 10w-30, the engine is consuming about a quart every 1-2000 miles after new seals and I have the usual 103 engine front seal leak and no major engine problems (knock on wood). I know I am just postponing the inevitable (a valve job) but, in the mean time and even after a valve job...WHAT WEIGHT SHOULD I USE WITH REGULAR DINO OIL?
By the way, I do change oil often but I am inclined to start using 10w-40.
Sorry for the long description but, I think it was necessary for proper assesment.
Thank you in advance!