I don't know if this is the same on yours, but on my 1999 there is an additional start relay (solenoid) mounted on the passenger side radiator support. It can be seen by looking in the passenger side front wheel well. This is a very bad location because its exposed to anything the tire kicks up, road salts, rock, gravel, water, etc... A common failure is broken wires and connections at on the solenoid. You can see the photos on my site.
NOTE - Ignore the red arrow in the photo, its showing where there was a missing bolt that holds the transmission cooler to the support. The solenoid is just below the red arrow.
The starter itself is also exposed to the same road crap, AND, it also gets cooked by the exhaust system. I installed a heat shield on my starter to help reduce the heat exposure.
Replacing starter on F53 – 1999 Southwind 35S