Vibration in steering wheel

My car is a 1993 toyota corolla with approximately 85,000 miles. I have always maintained this car. Within the last few months it has developed a vibration in the steering wheel not so much when in neutral but when stopped at a light and in drive. This has always been a very quiet running car until now. I brought the car to my mechanic (trustworthy and I have no complaints) for a tuneup as well to find address what the problem could possibly be (I was concerned it might be transmission). He did not feel it was the transmission and when performing the tune-up could find nothing wrong with the car. The only thing he could think of was it’s being engine mounts as they were dry and cracked. He said he could change these but “would not guarantee” that this was the problem. I had him change the mounts and it has made not one bit of difference in the vibration. He has told me my car is safe to drive. I have looked on line with others having the same problem and engine mounts always come up. Some say just have to live with it, others suggest putting the car in neutral while waiting at a light if it bothers you that much. I don’t like having and especially not knowing what is causing this vibration. Any suggestions.