This unit snaps down into the foil holder.  You can press the two sides at the top of the foil holder to take this out to clean it.  Not a OEM product but we have been selling this foil for years without any complaints.

This is the replacement foil for MODELS:

System 123
3550, 3525, 3512, 3510
3509, 3025, 3012, 3010
3009

Type:
5579, 5569, 5567, 5564
5479, 5470, 5469, 5424
5419