So what your saying is a fiddler, fiddled and now a tattler is telling. Be very careful. Normally a fiddler is content with fiddling with small relatively unimportant items. But when they are aroused, mostly by tattlers, they can be truly devastating to your happy home. They will leave nothing but devastation in their wake......I mean I think......well that's what I've heard....Who me? No I would never fiddle......well I guess I might you know if it was warranted. Which in all cases it is....Why? Well cause I said so tattle tail. Maybe the rubber needed to be ripped off. Yea, you never thought about that did you. God knows what would have happened if it wasn't fiddled with. So you just count yourself among the lucky to have a fiddler to save you and just forget about those dangerous rubber coverings.
Because you probably can't replace just the rubber covering. About the only place to check is the dealership and you know what that's likely to cost you.
There are places that provide refurbished key fobs.
Click the links below for a refurbished key fobs for your year and model. Around $50, Ebay will be the cheapest. Unless this is for an aftermarket key fob. Then you may need to go to the manufacturer for that.http://www.keylessremotesonline.com/2004-Isuzu-Rodeo-Keyless-Entry-Remote-hyq1512r04.htm
I do not know how old your fiddler is but I learned real quick that if I didn't fix what ever I fiddled with....well lets just say I walk with a slight limp. ";-) So depending on the age make them fix it.
I really hope this helps and good luck.
Oh and remember both Albert Einstein and Steven Hawking were born fiddlers.