Lexus: Steering wheel auto-tilt away

Last week the auto-tilt away on my '99 GS 400 started acting up. When
I put the key in, it wouldn't come down. After about a day it was
fine, so I chalked it up to it being cold that morning. Then it began
acting up again last night. Does anyone know what might cause this? Is
the tilt-telescopic motor going bad, and if so, how much does it cost
to get it replaced? Thanks.