I used to get about 18months – 2 years from shimano hubs, or about 2000 average miles. Deore didn’t seem to last as long as XT, but it’d be too small a sample size to say conclusively.
Not much that could be done other than spray with GT85, allow to dry then pack with exposed bit with grease.
I pretty much just use hope hubs now, they’re not perfect, but the customer service and warranty is brilliant. I had a hub go like Roter Stern’s* and they rebuilt the wheel and had it posted back in about 10 days, complete with an apology for taking so long!
*yes a £160 hub shouldn’t fail, but it was second hand, I’d had a good innings from it, and I’d say my riding must be pretty hard on hubs!