If you take the handle off the shower valve, you'll probably find a nut holding the cartridge in place. If you remove the cartridge and take it to a good hardware or plumbing supply house you can match up the cartridge with a replacement.
If you remove the window pane that's fogged, many glass shops can take it apart and reseal it for you. Do it soon, the moisture between the glass can cause etching that then requires the glass to be replaced rather than just cleaned and resealed.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI