O/D light flashes (sometimes)

I have a 1999 Ford Explorer. About two weeks ago my o/d light started flashing. I check around and people are telling me my transmission is gonna be toast. Shut the engine off went about my business and it didn't flash again for about a week. Came on again and same situation. The garage I bring it to says they can't know unless I bring it in when it's flashing and they can't see if my transmission is in danger of being ruined if it comes on occasionally. Any ideas?

Not true! With the proper scantool the codes can be read as long as you don't unhook the battery beforehand. And yes you will definitely make it worse if you continue driving...ask me how I know!

Welcome to this forum! Make sure that you have it scanned with a tool which is capable of reading manufacturer specific transmission codes. Driving with the flashing O/D light will cause the computer to go into limp mode (FMEM), and increase EPC pressure. This will put extra wear & tear on the internal parts.