Just bought 2000 Land Rover Discovery II

I took it to a mechanic and had a complete diagnostic done, and the code they found was 705, and they state it means that it's the Transmission sensor switch.   I don't know the history, but my buyers remorse is kicking in, and the mechanic says it's in great condition for being a 2000 and having 84,000 miles but I am really scared. This morning the Service Engine Soon light came on, and the (M) (S) mode were flashing. After turning on/off, they stopped flashing, but engine light still on. Please can anyone help me?

So is this your first vehicle? A few problems always show up on any used vehicle.
Does your mechanic have a long back ground in Rovers?
That 705 is not a big problem, just a mater of repair the circuit malfunction.
Is this your first 4wheeler, are are you going to use it for?
If your M S lights started flashing, most likely related to the circuit issue, but you might also check your battery, is it the original, are the cables clean and tight? The reason I ask is a low voltage problem will cause the M S lights to flash also.
How mechanical are you?

This is my first Land Rover. I will be using it strictly as a luxury vehicle. NO off-roading. The dealer changed the battery during my purchase, and the cables are clean & tight. My husband is the mechanical one, but our mechanic is at one of the best in town. (Washington state).
 
Thank you so much for your help. The email I sent you had a lot more info, but I forgot to come here to answer the email instead of answering in my inbox. I am glad that the code isn't major, but it's scary when you just made this huge purchase for a car you have admired, but never thought you could afford. Do you think the service engine light came on because of that code?