Related Clues:

• Sticky gunk
• Slimy crud
• Sticky, wet stuff
• Gunky stuff
• Viscous stuff
• Greasy stuff
• Thick, messy substance
• Grime
• Engine buildup
• Icky residue
• Engine fouler
• Yucky muck
• Sludgy stuff
• Tar, e.g.
• Mucky stuff