On three occasions over the past several years I have used the 'fix' described below by a Mandalay forum member. Since I live in California I believe the issue is not so much dirt and moisture but more likely the heat drying the lubricant. Whatever the cause, on each occasion the problem has been solved. I also use motorcycle chain oil.
'One of the things I have had to do a few times is to crawl underneath and tap
gently on the lever that extends from the step motor while my wife opens and
closes the door. Be sure to be out of the way in case the steps deploy. This
has happened a couple of times after I have gone through heavy rains that washed
a lot of grit into the step mechanism. Once the steps open, I thoroughly
lubricate everyplace two moving parts touch. I use either motorcycyle chain oil
or a good quality silicone spray'.
Good Luck and I hope this helps,
Paddy Drumm