Sorry, I'm not familiar with Pentosin, I don't know what it is. Overall, it's best to stay with the recommendations in the owner's manual. Some tweak things a bit by going over and above what they really need, but using something that doesn't meet with the manufacturer's specs is not the way to go. If this Pentosin isn't the right stuff, then I imagine a complete flushing of the p/s system wouldn't be that big a job, or that costly, considering...