I had these 2 same problems, 6 years ago on my 1995 Range Rover.
1. The relay (Siemens, not Lucas) for the intermittent function was working irratically. I replaced the relay, and that cured the intermittent function. This is the easy fix. No problem since.
2. The contact and contact plate inside the wiper motor were slightly pitted, and the wipers would not park in the off position. I had to remove the hood and the decker panel to remove the wiper motor from the firewall. I drilled out the rivets, in order to get to the contact and contact plate. I polished the contact and contact plate to eliminate the pitting. I packed the contact and contact plate with dielectric grease, reassembled the wiper motor, and pop-riveted the wiper motor together. I reassembled the wiper motor to the firewall, the decker panel, and the hood. This is the hard fix. No problem since.
Hope this helps.
Jim Lupinetti