There is a way to check. Put the boom all the way down. Unhook the line at the back of the cylinder closest to the motor compartment. Wipe fitting on cylinder clean and on loader frame. With loader running push the boom pedal for down. Make sure you only push pedal in down position since the other way will spray oil out the open line. Check open fitting on cylinder, if oil has come out of fitting you have internal leak. In all honesty if the loader cylinders have never been resealed you might better take the time to put new seals in. They aren't that expensive and not that difficult to install.