If you just want to add a bit more Castor, go down to the drug store and buy a bottle of castor there. It's a finer grade than use for fuel, and no aditives. Hang on to your check book though, It cost me about $6 for a 6 oz bottle. You might check with one of the club guys. A jug of castor was common stock at one time.

What engine are you running that requires 18% and is it for break in or standard requirement? Also, is the Wildcat fuel a mix of castor and synthetic or straight synthetic. If it is a blend, adding an ounce or two of castor will be OK. I would hesiatate if it is straight synthetic. Some synthetics are not good mixers with castor and the last thing you want is a jug of goop.

Let us know about the engine and fuel mix in the wildcat. It may be that it is good to go right out of the jug.

Don