It can get in at times. It can corrode the screw terminals. Coating them with dielectric jelly and wrapping the outside cover with electric tape helps.
Don't know what actuator you're working with but on my Von Weise movers I drill a SMALL hole (1/16" or so) in the BOTTOM of that cover to allow water out should it find it's way in. The Super Jack movers I've seen already have a narrow slot made into the bottom of that cover for that purpose.
It is a super jack and I saw narrow slot and I think all the water drained out I thinking of taking the cover off and letting the sun dry out the motor connections
The petroleum jelly is a great idea. I often spray connections with silicone lubricant (aerosol can) which repels water and doesn't seem to affect plastic/rubber wire insulation etc, but only as the last step as you don't want an insulating substance in between contact areas.
Spraying the terminal strip with WD40 also helps and isn't quite as messy as the jelly. I do use the jelly in all my coax connections though and over the past 14 years it's worked well.