On Thursday, 25 February 2016 13:38:56 UTC+2, Casey wrote:
I think the reliability of a FES would be more reliable than conventional motors due to less parts. However, over the long term a concern I would have about FES would be water/dirt/debrie in the motor and electrical components, assuming that not all are shielded and even then the deterioration over time.

It all depends on the design and materials but people are happy to drive EV's (like one's from Tesla) through mud, water and other harsh environments for years on end without trouble.
Our gliders see a bit of dust for a few seconds once or twice per weekend so I'd hardly worry about it.
I've seen brushless motors run for years in extremely harsh environments without any maintenance and servicing. If the design is right, a brushless electric motor should outlast a combustion engine many times over even with zero maintenance.