Is it possible to drop in and out of an existing recorded track to make a correction overdub or must it be a new track?? Being a rubbish guitarist I end up with far too many tracks.
Silence the bad bit, then record the “drop-in” onto a new track.
What I generally do is to work with one “master track” (the original recording) and one “Take-two” track. After making a new “drop-in” (which will be on a new track below the “Take-two track”, drag the new bit up into the “Take-two track”, then delete the (now empty) track. (Use the Time Shift tool to drag clips from one track to another. The shortcut key for switching to the time shift tool is F5)
Thank you for your reply, that seems like the answer to avoid having 10 tracks with a few seconds on each. 
There are other ways to do it - that’s just the way that I usually work.
An alternative is to select from just before where you want the drop-in to just after the drop-in on the “Take two” track, then press Shift+R (Append Record).
This method is a little quicker to execute, but the disadvantage is that if you need to adjust the position of the new drop-in, you will first need to “Split Delete” the silence that joins it to the previous drop-in. (try it and you will see what I mean). I like the first method because it gives me separate audio clips for each drop-in, so I can make all of the drop-ins, then go through them and trim / tidy them as necessary.