I think the waterblock idea is a bit overkill (no to say they don't work, they do and well) its just not necessary . The WVO will be flowing past the trip rather fast so damage to fuel is extraordinarily unlikely (vaporization won't be a factor) and heat will get transferred to the pipe which will then be conducted into the oil. The pipe design is cheap and easy and works well enough that there is no real reason to lathe out a block design.

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'84 190d 2.2 - Silver
Converted to 5-Speed
'84 190d 2.2 - Blue
Factory 5-Speed

'76 300D (W115)
Sold, found again in less auspicious circumstances