I have used the Auto RX product.
I would NOT put engine flush products or diesel fuel into the oil.
You buy Auto RX online from their website.
Follow the directions on their website.
I have also used this product, as instructed on their website, for my automatic transmission.
The only varience I did was I had it in there somewhat longer then they specify and I also had a Magnefine filter installed in the transmission fluid cooler line.