hello i have a b20 kubota .dont know what year it is cant find the serial number for the tractor . it has a kubota fel and a kubota subframe on it .no back hoe.the engine is seized is it worth rebuilding . are parts available for the motor?the former owner ran it without engine oil. it had a engine oil leak. the motor is a d950-a-t. is there another model motor to swap it? what does the a- t mean in d950-a-t. it is 4x4 hydrostatic drive.any help would be greatly appreciated thank you .