1194 case tractor (transmission filter)

I recently bought a case 1194 tractor with less than 400 actual hours. I was told it had been recently serviced and the fluid levels all checked out ok. From all appearances the tractor is like new. I have used it a few times mowing and with the 56L front loader and it works like a charm. A few days ago the transmission filter light came on and friends recommended I change the oil and filter. Local Case dealer fixed me right up and I now have fresh oil, new filter and the LIGHT IS STILL ON. Operating it as per the manual does not make the light go out and everything still works like a charm. I looked for a sending unit suspecting it might be the source of the problem and located what appears to be a sending unit on the back part of the transmission directly above the front of the drawbar. My question is actually several rolled into one: is it safe to use the tractor since the filter and oil are fresh? would a defective sending unit default to "light on?" and is the unit I located actually the sending unit?

Any technical advice would be appreciated.