Historical clue formulations

• Greasy goo — 2020-11-22
• Residue in a bathtub drain — 2015-11-17
• Engine buildup — 2013-12-28
• Sticky matter — 2007-10-15
• Icky stuff — 2007-09-25
• Slime — 2006-09-16
• Unwanted buildup — 2006-03-01
• Icky stuff — 2002-12-06
• Crud — 2000-06-07