unless you have good mechanical skills and a workshop manual don't try it cos you will do more damage they fill up with oil so if not service regularly the oil port to it clogs up you are better off changing oil and filter adding a pint of ATF to it this goes through the oil system clearing sludge and I use it quite often to fix this problem if all else fails you can take to an engineering firm (car) and get them to take your old 1s appart and clean em and refit em at a fraction of cost of renewing
peesian
April 2010