Mark, I've done a bit of research on the internet after reading your story. I've found several reports and stories of Reese units failing but have seen good reports for the Master Lock units. I'm going to go ahead and purchase the Master Lock that I had before. It it the entry level model but has worked well for me for over five years. I also like that it has its key slot facing perpendicular to the pin. This is the one I had and am going to buy again:
Products - Towing Security - 2866DAT - Master LockŪ
One thing I have done is to unlock the lock at least once a year and lubricate it with Tri-Flow =click
which is a lubricant that a locksmith recommended to me years ago. I use it in several locks so it's not just for the pin lock. However, any type of lubricant would suffice, I would imagine. I'm thinking that's why mine has lasted over five years and still was performing well.
The problem with leaving a hitch pin lock unattended for years, even though it has a cover over the key slot, is that it can seize and be difficult, if not impossible, to remove and you may end up having to cut through the pin or drill the lock out in order to remove your tow bar if it needs to be removed. That's why I like to lube the lock every now and then.
And I'm not saying that is the reason why yours failed but my concern is more for the fear that it will seize when I want to remove the tow bar. I actually remove my tow bar to clean and lube it twice a year as I sometimes like to do it in a garage or some other warmer place than when it's on the back of the motorhome.
eta: here's an example of a guy who had to drill out a Reese because he couldn't get it off: