compare radiator sizes for your car and other 124s. if the bigger engined cars havea bigger radiator thats the first thing i would do.
use less anti freeze in the coolant. unlike what some people here think it doesnt have good heat transfe capability. i use 100% water in my car. but i live in sunny southern california.
keep your car tuned up.

you can use any oil cooler as long as you hook it up correctly. yuo do not have to buy a mercedes unit, it could be a vw, citroen, toyota unit as long as it looks like a mini radiator and can flow oil its an oil cooler. install behind the bumper, use appropriate hoses keep oil fresh.

also, using an oil cooler will allow you to add a little more oil aiding in heat transfer.

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'O=00=O'
bmw 2002.
long live the legend