I just replaced the tank in my 70 B. From what I read, I should have had a vented tank, but mine was unvented. The Carbon canister had been pulled from my car, so even if I wanted to put in vented tank I had nothing to vent to! I checked all the options, such as having my tank fixed ($300 I was quoted!) and complete replacement was the most economical way to go. I couldn't believe how bad the top of my old tank was when I finally got it out. A big rust bucket! Except for a stuck bolt here and there is was relatively an easy job. I did it in a less than 2 hours. If you do decide to do it, I would recommend replacing the sender at the same time. It's $20. I would also recommend getting the fastner kit. Another $9 well spent. Also, rust proof your new tank with POR-15 or something similar and it should last another 30 years!