Septic tank possible leak.?

My drains were backing up so I got the septic tank pumped. There were a lot of roots in the tank, but also it seemed that water was leaking in from the bottom of tank, and he told me I should get a new tank. There's been really a lot of rain in the last few months. Since pumped I am not getting anymore backup. I don't know if I really need to replace the tank. Could the water in the bottom be coming back from the leech fields due to all the rain? How do I know if it is a crack in the tank or not? It is a concrete 300 gallon old tank. I think the guy might've been trying to take advantage of me and my lack of knowledge about it all. Since pumped a few days ago, someone looked and said the water is at the right level. So, I am mainly concerned about the water I saw running in at the bottom. Any help would be much appreciated.