My Mom's '97 Buick LeSabre with 112,000 miles has started to act a little funny when I first crank it up and start to back out of garage. Sometimes when I put it in reverse nothing happens. If I give it a few seconds, everything starts working properly. It only happens when it has been sitting for a week or so. She doesn't drive and I try and take her car out a couple times a month. Any ideas?