I picked up an 05 that I think the PO put head gasket sealant in the radiator fluid before he sold it to me. I'm planning on having the HG done as soon as possible. Truck (V6) is sitting at 218k right now. My question is how long will this HG sealant work? I've already put almost 2K miles on it in the week that I've had it. I'm monitoring the rad, oil, temps and checking for codes. So far, all is clear.