It tries to start, makes a noise while turning somewhat, turns on and
off a few times, and then gives up. Then after around 10 minutes it
leaps into action and works perfectly.

What's happening? Its clear from debris and leaves. The inside furnace
is new (2004), but the outside one unit is older than that, but it
doesn't look all that old. Do these units need to be oiled or serviced?

Thanks for any help,

Dean