I suspect that you have a KTCXO3 that the internal oven is not working. If your rig is still under warranty (I suspect not, judging by the SN) you could contact Elecraft, though I doubt that they have any working 1ppm oscillators (I tried to order one recently).
The other option may be to order one from eBay. There is someone in China that is selling a knock-off of the KTCX03 for about $50 that may work for you.
You can actually test the drift on your device by installing WSJT-X and using the "FreqCal" function in the "Mode" menu and select 7.850 CHU or 10 MHz and watch the drift over an hour, as you start your K3 up from cold. If you get fancy, you can even put the data into an Excel spreadsheet and plot it in a graph.