This has probably been read before. But I found this nice section of the Cosmoline Removal post on www.surplusrifle.com. It pertains to removing cosmoline if you don't want to also remove the original finish. Like what happens when you use brake cleaner or put it in the dishwasher:
"The stock is a different matter. Water and harsh chemicals are simply poor choices for cleaning wood. Chemical companies have been working for many years to develop cleaners for wood, only a few of which are water based. Murphy's Oil Soap is one such product that can be used in reasonable quantities on wood. The heavy duty "green" and "orange" cleaners are simply not appropriate for cleaning wood stocks. They contain harsh chemicals that are absolutely not necessary for cleaning cosmoline. So if your objective is to do nothing damaging to the wood while simultaneously removing the cosmoline, do NOT use any water based cleaners and avoid "grease cutters" like oven cleaners. They are extremely harsh chemicals (like, why else are you supposed to wear gloves if they aren't harsh?) and are NOT GOOD FOR WOOD.
So, let's explore the correct way to remove cosmoline. As mentioned above, gentle heat is by far the best way to liquefy and remove cosmoline. If your oven is big enough you can put it in there at "warm" (lowest possible oven setting) and it will bleed the cosmoline out from the pores of the wood. Wipe it down every 15 minutes with old toweling until the weeping has stopped. If that won't work due to size or domestic issues you can put it outside in a plastic bag, some people like black because it absorbs the heat of the sun better and some prefer clear because they opine that the direct sunshine generates more heat. This will take a little longer but it's important that whenever it starts to cool down that the stock be removed and wiped dry. I kind of like the creativity of the "dashboard" process which is a sheet of tinfoil bent up to hold liquefied Cosmoline and set on the dashboard of your vehicle. I haven't done it but it sounds like a great plan to me if you have a place where you can do it without tempting someone to "borrow" your stock. The latest method is a wrap in rags, VERY tightly sealed in a plastic bag, and a bath in the hottest water you can get. Haven't tried that one but it sounds pretty reasonable to me. Word has it that you can add boiling water from your stove to the hot water from your heater and get pretty satisfactory results.
I am going to build a "cosmo coffin" that uses light bulbs for heat but haven't done it yet. It's one of those projects that I'll get to when I get a round to it.
Word of warning - When baking your stock make absolutely sure that it's positioned in a way that will keep it from close proximity to the coil. I understand that modern gas ranges have plates above the burner so they should be fine as well. Also, if you are using a rag to remove the stock and/or hand guard from the oven, and the element is in the heating mode, if the rag touches the element it WILL begin to smolder, virtually immediately. (Please don't ask how I know.)
The point is, GENTLE heat will melt cosmoline away from both wood and metal with NO ADVERSE AFFECTS on either the wood or the blued or bright metal. After a couple of hours of 15 minute heating cycles, wiping between cycles, just let it cool and wipe off any remaining surface cosmoline with mineral spirits.
It's also a good idea to keep ANY solvents or cosmoline out of your drains. They are petroleum based and float on water. This means that they are not going to flow easily through the traps and are likely to gum up and/or clog drains. Everybody has to figure out the best disposal method in their particular circumstances.
So, that's about it. If you want to put your mil-surp rifle back into the condition it was in prior to going into storage, be patient, be gentle, and be thorough. You will ultimately be very, very glad you took the time to do it right, the first time. And if you are going to refinish you will not be disappointed by having the cosmoline seep up into and/or through your finish of choice. When you do it right you will find that the stock will take just about any finish that you like."