Odometer works on and off .... Speed odometer always works . Any ideas ?

No, when odometer stops that stops as well ...... but as i said speedometer never stops working

Replace instrumen cluster! .. Salvage yard or eBay best source... Record mileages on both clusters so that can be deciphered as needed.

I had that in mind as well .... I went even as far as checking plastic gears inside cluster as i have read sometimes one will break etc......nope...... Also wondered if it was just happening when it rained as that was case for a bit until it went out when not raining. To go along with all that ... I hit a railroad track one time and it went to working so i was suspecting harness , connections,etc.....cleaned all them and wires coming into connector didn`t seen to have any loose.....crazy car ......lol