Hi,
Just to further tout prochems products. We use Citrus gel on grease and tar, as it works very well and smells nice.
Its made from terpenes, so you can even hammer down the organic angle if you like. We have tried solvall and solvex, but it falls to the base of the carpet easily and could (potentially) disturb the integrity of a tufted construction. ie dissolve the latex. The gels are easier to manage in my opinion.
Just make sure you rinse it well or the amyl solvent component will resoil like mad.
Hope this helps
Graeme
Access Cleaning Solutions