How can I determine if my septic drain field needs replacement?

So last week I noticed there was a puddle of water on top of our septic tank, which was gone by the morning (few days before that it rained hard all day and most of the night – I figured water must have somehow seeped in at the top of the tank).

I had someone come out and pump it and when they opened the tank it was full to the top, and once they drained it to under the outlet there was a trickle of water coming back into the tank.

The contractor then proceeded to tell me that my drain field had failed and I would need to get a new one installed. (It's only 7 yrs old). I tried to ask whether maybe some sludge went into the outlet and blocked it further down the line, but they weren't too interested in listening to that.

So I decided to start digging up the drain lines, but I haven't come across a D-box nor any other pipes that have branched off. (There are supposed to be 3 pipes out there.) It looks like only one 50 ft line from the tank, but that one line I have located I dug down to a few of the drain holes and there is waste coming out. The top of the leach field looks completely normal,no standing water or sogginess. (Also our septic tank has 4 big slabs of concrete at the top, and I have a log mover on the way so I can get the tank open.)

Even when I spoke to a septic guy over the phone and explained what has happened he was adamant that I need a new field. When I tried to ask if maybe something went down into the lines or maybe roots had grown into them he didn't want to hear it; he just said the field would need to be replaced.

In the meantime I'm going to be adding a elbow at the end of the drain line for an inspection/cleanout, then getting a camera down there. I am just trying to get some no-BS answers without someone trying to sell me a new field!

Any recommendations on how to proceed?