This is a difficult situation... but you can remove excess oil or other liquid contaminants from the holster by filling it with Cat Litter
(make that CLEAN and DRY Cat Litter) <img border="0" title="" alt="[Eek!]" src="eek.gif" /> and then placing the holster in a small bucket and filling the bucket with the same material. Let it sit for a few weeks in a warm dry place and the dry material will leech the oils out of the holster. When you retrieve the holster, dump out all the cat litter material and clean with compressed air, and a dry shoe buffing brush. It won't be new, but at least the excess oil will have been removed from the leather and won't continue to soften it. The nice thing is that this process is completely non-destructive... AND you can still use the cat litter for it's intended purpose
I know that our member 'GT' used this process to salvage a hardshell holster not too long ago that had previously had some type of oil generously applied to it...
Good Luck... and let us know how it works for you.