I have a 78 super beetle with only 27000 org miles. it had a bad frontend shake between 50 and 60 miles per hour! last year i replaced the front bearings and that seemed to help but only for a shoert time. Can be very smooth but when the shake hits very bad! Do i need a whole frontend replacement ? jbugs has a kit with poly instead of rubber. what is the main culprit and can I just replace that? Also the passenger seat rail has come apart, any sugestions where to find that. Not many miles but rubber does get old and brittle!