It was such a pain to remove the rubber boot on mine that I only serviced the left motor. After this initial repair right motor was noticeably slower until it also failed. So while you are there, just service both of them.
Mine don't have boots. I'm not sure why. 1997 UK spec. Both headlamps rise and fall at the same speed. I wonder if the left-hand motor gets more crud thrown at it because, in the UK, it's the one closest to the kerb.