A crack at the joint between the filler neck and the tank is a very common problem on the sedans. After filling up you will probably find that the base of the filler is wet with gas, while the area around the cap and the neck itself are dry. Danny's repair is just the ticket. If you can't do the work yourself, often a local radiator repair shop can help you out. Repair is probably less expensive than replacing the tank. Although I've not had this done for some time, I've had this problem on both of the 122s I've owned.