511 Impregnator is the best.
It's about $100 per gallon
After the material is clean, allow it to dry for three days and protect it from staining.
Wear gloves, soak a clean white cloth in sealer. Saturate the surface.
It should turn "darker". After it sits for 5-10 minutes, buff with a dry white cloth. Thats it. It should last for at least 5 years.
The stuff is CRAZY stinky. Might consider a respirator if you cannot get fresh air flowing.
KT