Having just had my main sail manual furling gearbox apart, I know on mine there is no worm gear, just two spur gears. Which makes sense, because you (usually) can not back-drive a worm gear.
Were there different models? Or are you thinking of something else?
On all of these gearboxes it is critical to consider all the lip seals maintenance items that need to be changed on a regular basis. I have mine on a two year replacement cycle, which is probably excessive, but seals are cheap and readily available, and gears are NOT. If you see even a trace of rust on the seal, that means the garter spring is rusting and failure is imminent. Replace it sooner--not later!
When changed it is also important that the seals be packed with grease so they do not run dry, even if you use oil as the primary lubricant in the gear box. In addition to lubrication, grease helps make a good water barrier. On the seals that face upward, and are subject to the most persistent saltwater contact, consider going with double-lip seals instead of single for an additional barrier to water, dirt, and salt.
Spanish Wells, Bahamas