Ooooooooo this is as good a value as Theater Popcorn and Ball Park Hot Dogs. Or that portion of the fortune from the son of the now deceased king of moogooboogoo Nigeria.
I would go for the plan as offered above: "Do it for free or watch my tail lights".
But beware. They WILL NOT DO IT, they will make a mistake and "believe in their heart and soul that the preservative was applied". Aw gee whiz. Be there when they do it. Examine the rig closely, before and after. MAKE THEM WRITE ON THE SALES CONTRACT THE PRESERVATIVE WAS APPLIED. Then you have them by the hurtin' hairs.
Like the time I purchased a used car in the Bay Area. Car had "17,000" miles on it. Got home and found a sales receipt under the spare tire from the dealership three weeks before showing the actual mileage at 79,000 miles. The dealer had fitted mew brake and clutch pedal pads and charged the customer for them while doing routine service. The receipt advised "Suspected transmission countershaft bearing failing". I took the car and the receipt to the Alameda Country District Attorney. I was 18 years old when I got my first, and lasting impression of automobile dealers. Of course the dealer tried to slime his way out of it. But they had already sold my trade-in. The Assistant D.A. told them "Make This Man Pleased (I was a boy)". They signed the ownership certificate over to me, and fixed the transmission at no charge. I had to pay 21 dollars in license fees. Then their slimy finance company partner demanded I had to pay for the car. A couple of deputies sent to their office fixed that problem.
So I remain leery of "New Car" hustle. Ninety percent are sleazy.