Looks like the thermostat housing on the front of a TAMD 41. Just a good flat spot to place a sticker. Refers to crankcase oil used in the sump. When the engine was built, CD oil was the most modern. Since then oils have improved and the API CD classification is obsolete. Any modern diesel engine oil will be fine. SAE 30 or SAE 10w-30 or SAE 15w-40. The latest API rating for diesels is CK (I think), where the second letter is the series. CD was followed by CE, CF, CG, etc, up to whatever it is now. The modern oils are fully compatible with an older engine spec'ing CD. Check the manual to see what viscosity to use. Might spec a SAE 30 or a 40. If it specs a 40, a modern 15w-40 will be fine. Straight SAE 40 is thick as honey when cold, not good.