I think I have the solution.
I rebuilt a window like this that was fogged. I had the opposite problem as I had much difficulty getting that bar off the window glass. When I reassembled, I threw away the tape seal originally used on the bar to window joint, cleaned the window, cleaned the bar, and used the same sealant that was used on the window seal as glue to hold the bar to the window. It has held up since July of 2012.
The sealant for the windows is C.R. LAURENCE 877 CRL Super Spacer Sealant, which is available from Amazon.com. It's was about $13.00 per tube in 2012. It may also be available on Ebay.
If you can remove the bar, get all of the old tape removed, and be able to clean the window surface and the inside of the bar, then this sealant should work for you without removing the window from the RV.
If you can not remove the bar, you will probably have to remove the inside window trim ring, push the window outside (have a helper), remove the screws at the bottom of the window frame to allow splitting the window frame wide enough to remove the slider window, and then remove the window from the frame. Once removed, it will be easier to work on removing the bar, cleaning everything, and gluing the bar back to the window using the sealant. I had to use a lot of heat (heat gun or hair dryer) to get the bar removed from my window.
If you remove the window frame from the rv, be sure to reseal the window frame to the RV upon reinstallation. I used putty tape from the local rv store as a seal.
After you apply the sealant to the bar and window, push it back together, maybe apply some tape to hold the bar in position on the window, and let it cure for 24 to 48 hours before reinstall.
If you get sealant on the window outside the area covered by the bar, it is easily removed with a razor blade after it cures.
I hope this works for you.
Fred