How to descale and maintain Gaggia Classic Espresso Machine - iFixit Repair Guide
Got this Gaggia Baby Millennium for only $40! one set of gaskets and a descale and it's ready to go! (more info and resources in comments) : r/gaggiaclassic
The Concise Way to Descale the Gaggia Classic Pro - YouTube
How To Descale Gaggia Espresso Machine The Right Way