I work for Yales brother..I have 8 PSI trucks in a 24/7 operation that is hot and dirty. Have seen many coolant tube issues and also water pumps ' Trucks are 1.5 years old and some are near the 8000 hour mark. I have not seen any oil use in any. Have seen oil leaks at filter fittings but no big usage as you describe. Only other issue on all units was fault code running rich. Tried a few things but did not resolve issue. Opened up mixer and found propane oil and dirt build up on the bulb of the diaphragm. Cleaned off, put back together and all running fine again. Diaphragm was heavy and not moving properly. Saves wasting customer money on new mixer.