Ofcourse not good but how bad to drive say 300 miles in limp mode with a suspected bad L/R Selnoid?'

Was not able to get appt at dealer and ONLY truck so had to drive and probably drove way 300 miles till I got it to dealer to find out that I need a new LR selnoid. Did I damage my tranmission too bad by doing this?

Also how much to people see this part going for...dealer said its about a 400 part. Just following up on them as its a new dealer.

Thank you.....