Dota 2 Guide - How to watch old replays in Source 1
Download this into an empty folder: https://drive.google.com/uc?id=0B8ZNo...
Extract it. Go to Steam, right click Dota and choose properties. Browse local files, and copy dota/replays to the Source 1 folder. Start the Source 1 dota.exe and load any replay from the Watch tab.