our d6 r series II with a C-9 has had the oil plug repaired before we acquired it and it has always leaked alittle. Some say to replace that pan engine needs to be pulled, others say not. Anyone had a personal experience?
No need to pull the engine
Without S/N or at the least the "prefix" can't be 100% sure but the one of many D6 R II tractors I looked at other than maybe dropping the belly pan the only thing you need to do is drain oil and remove pan bolts.
On our C-9 equipped D6T's the pan can be pulled without removing the engine. We did three last year if my memory serves me correctly. All caused by the machine running up to the nuts in mud and getting the belly guards full. Once it dries it's like concrete, after that a good whack on the belly guard with a big rock or a tree stump and the result is a cracked oil pan.
CASEIH had a similar issue in the on 2nd gen Magnum tractors. Over time, lube seepage on the sides of the block would cause dust to accumulate to the point where the oil pan became wedged between the frame rails. The engine was rubber pad mounted so movement from normal operations would eventually tear the pan off all together. That was a pull the engine repair. Best practice is once a year, drop the belly pans and clean. Sage advice
If it's like the 6R I had AAX series, it had an NPT plug. I always wondered why, Cat had straight thread plugs with a copper gasket forever why change to NPT