I've just aquired a 1976 300D and am having trouble with a slipping/flaring transmission. Are there any adjustments that can be done? It's not setup like the 123's.

First check your fluid level- too little or too much will definately cause flaring. Secondly there is quite a set of mechanical linkages which can affect how the transmission shifts. I adjusted those on mine and it greatly increased shifting performance (but frankly I don't quite remember which linkages it was that I messed with.)

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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