I use dawn dishwashing liquid on greasy stains. We love pasta dishes and between 4 kids and a husband who continually "miss" their mouths, we have this issue 3-4 nights a week. A little squirt, let it sit a minute or two (longer depending on how set in the stain is) then rub out under the faucet, clean as usual. This also works on grease stains when my husband works on the cars or changes the oil and drips.
I use regular shampoo for greasy stains and anything tomato-based. I discovered it accidentally when one of my kids spilled spaghetti sauce on a white shirt and I was out of pre-treater and laundry soap, and the closest thing at hand was shampoo. I figured it was better than nothing, and to my amazement, the stains came out completely! Now I use it for a lot of stains, it works great and it's a lot cheaper than pre-treater.
I just bought some Zout spray stain remover (available at grocery stores, e.g. Wal-Mart) which has three enzymes for three different kinds of stains, one of which is greasy/buttery stains. I can't say whether it'll work for you, but seeing as this is a frugality site, I'll say that currently you can give Zout a try for "free" because they have a rebate going on now where they'll reimburse you for the cost of the Zout (minus tax and minus the cost of your postage stamp).
I work in fast food, as do 2 of my teenagers. I use K2R spot remover to get out oil stains. I can only find it at Drug Mart, here in Ohio. I spray it on and let it sit for at least 12 hours, then wash as usual. Repeat if needed. I have even been able to get out stains that have been machine washed and dried. Good luck.
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