I just found something called Motorcraft XT-M5-QS, It's a Ford factory fill and used in their heavy duty truck manual transmissions (so it's meant to take a beating).

Now, I say truck, and you think of a heavy, viscous oil unsuited for regular cars. This oil is all the rave on the Mazda forums - guys who drive MX5s, RX8s and the like, both on the street and track. Everyone is reporting that previously sluggish and slow manuals were like a new transmission after filling this oil.

I don't know about you guys, but I'm definitely going to head over to my local Ford dealer and see if they don't have this fluid for sale.. It's apparently expensive, but I only need 2 liters (1.5, but, you know, nothing's sold in 1.5 increments :p), so who cares.

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1987 W124 250D
- 387000 miles
- naturally aspirated
- European
- 5-speed manual
- ASD