1993 Regal Strut/ Shock Replacement

Hello-My son has a 1993 Buick Regal-6 cylinder 3.8. He decided to replace the drivers side shock which basically is the replacement cartridge that fits into the housing. He got that replacement in and when he drives it there is a pretty bad shake or vibration coming from the front. It almost feels like a wheel that has a serious dent or out of round. Multiply that by about 100 times!! I asked him if he had replaced any oil in the housing when he put the new one in and he told me NO. Could this be the problem?? Not enough oil in the housing??
Thanks for your help!!