You need to clarify this one where is the turbo located if on the top of the blower it drains through the blower,the turbo is pressure feed if the return is stopped up it blows the seals,do you check the engine oil through the fill tube or does it have a different stick photos would be nice to help I see no reason for a fill tube to stop up unless a rag , the seal or lid from a jug of oil some how got in there a oil jug lid is just right to plug the 1 in hole but the turbo should be blowing oil out of the tube if it is tied in there
If you are close to Miles City I have a friend there that may could help he has a 8V92 his Eagle
good luck