I doubt Gates is OEM but they are high quality, usually American made. I've had no issues with them and I have used them on several cars.

MB would more than likely get their hoses from ContiTech, not Gates who are a US based company. Although Gates no doubt make a replacement hose.

The MB EPC comes up with the same number for US W123.133 300D's (with A/C) as other chassis models without A/C. This is OE part from a US supplier.

Just looking at my own hose - can't see why with or without A/C would make any difference?

I would buy a cheap Uro 1235011882 hose and see if it fits. But maybe you have already bought something?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5