Honda Accord Rear Engine Mount

My 1991 accord automatic vibrates excessively when stopped in gear and violently when stopped and in reverse. I believe it may be the rear engine mount (hydraulic mount). I brought the car to my mechanic and he stated that there is an "involved process to evaluat the mount". (The problem might be the vacuum or the hydraulic unit) The Honda factory service manual gives no information on how to diagnose or change the mount. Can anyone help me?

Neil