Volvo 2001 V70 transmission probs.

I have a 2001 volvo v70 with 109,000mi that was totalled then rebuilt by the insurance company. I just recently had the lights go on to check the transmission. I brought it to aamco and they ran a diagnostic. They told me I was tripping two codes I beleive one was gear or clutch slippage. Noothing was wrong while driving the car other than the warning light being on. They said my fluid was low and burnt. They want 600$ to open the transmission up and find the problem. My question is can there be lights going off for minor things where maybe I could just change the fluid and hope the problem is rooted in the fact that the car was totalled or is this something that should seriously be attended to. Any advice would greatly help since I cannot afford to be wrong. Thank You.