I bought my 51 8N about 5 years ago and have changed oil regularly. It does use a bit, perhaps a qt. in 40+ hours. I've noticed that my oil filler pipe seems to take oil slowly. Is it common for them to get plugged? What might cause it? I'm due for an oil change and would like to remedy the problem. Suggestions? The old gal is getting kinda tired but with 10W40 Detergent she holds decent pressure in fairly light duty, i.e., brush hog and hauling a 150 gal tank of maple sap through the woods in sometimes deep snow and or mud. .