I have a 1992 300E 4-Matic. The 4-Matic warning light came on about a month ago and I took it to the dealer who 'reset' it for about $150. Well, the light just came on again, disabling the 4-wheel drive system (which is unfortunate given that I'm driving in upstate NY with snow all over the place). Is there a way for me to reset the system... is there a tool I can buy to do it? Also, any guesses as to what the problem is? I know the transfer case was replaced on the car at about 110K miles. The car now has about 220K on it. Any particular issue I should have a mechanic look at?

Thanks for any help!