[Lil bastard]

It is a silicone sealant. RTV stands for Room Temperature Vulcanizing. Most general purpose silicone sealants are RTV type. It generally uses an acedic acid based solvent and is characterized by it's vinegary smell.

This form of sealant starts to cure as soon as it is exposed to air/moisture.

There are several types of silicone sealant.

Anaerobic silicone is usually 2 parts which must be mixed together and sets quickly. It does not require exposure to air to cure. It is often used in sealing engine halves, valvecovers, etc. where the silicone is pressed between 2 surfaces and not exposed to air.

UV or Radiation silicone sealant will only cure under exposure to ultraviolet light.

There is also Thermo or Thermoset silicone sealant requires exposure to heat in order to cure.