You don't need to worry about the age of a Raymarine
linear drive if you can examine the innards.
You do need to verify that Linear Drives more than 15 years old have their planetary drive gears converted to bronze
because they originally came with plastic gears which were very easy to strip. (Personal experience 1/2 way between San Diego
and Cabo San Lucas).
I have stripped and rebuilt our 1994 Linerar Drive twice - once in Dec 2001 to replace the stripped gears and again in spring 2013 to install a Type II (twice the power) motor
Everything inside looked perfect in June 2013. The gears and drive belts looked new, there was no lash in the gear
mesh and the belt teeth were all sharp and clean.
That Linear drive has 2800 motor hours on it and over 5,000 sailing miles on it.
Good luck finding a used one - as far as I can tell the new ones are just like the old ones so folks like me that recently replaced their course computer and control head
just keep their old linear drives 'cause they are so solid and reliable.