Mostlikely a sight glas is on their instead of a dipstick so that the systme is guaranteed sealed. Don't get me wron a dipstick will seal it but a dipstick can be lost or popped off plus to check it you have to wipe it off and put it back in to check it. Not that that's a problem because I don't mind getting my hands dirty, but a sight glass all you have to do is look at it and if the level is ok then you're good to go and you don't have to worry as much about dust and other contaminents getting in from your wiping rag or whatever. Also if you were wanting to check and see if the level dropped off when using your lift or aux. hydraulics you could watch your sight glass.