The lift doesn't work
In THE LIFT, standing on the platform and pressing up does nothing. Seymour sighs: "ITS NO GOOD! THESE THINGS NEVER WORK.."
Nudge 1Where to look
It's not broken beyond repair: something is just loose.
Nudge 2A stronger push
You need a tool. It's up in the trees on the jungle backlot, in a hut at the very top.
Nudge 3Almost there
The hut is in ISNT THIS HIGH?, reached by climbing the trees from MGAMBA TREE HUTS. The jungle is behind Tarzan, so see Tarzan won't let me past first.
Show the solutionThe whole answer, with a video
Bring the spanner from the tree hut in ISNT THIS HIGH? and walk onto the lift: "ILL JUST TIGHTEN THIS BOLT HERE..". From then on it works: stand in the middle of the platform and press up once for each stop (down to go back). It runs through three rooms, THE LIFT, FIRST FLOOR and TOP FLOOR, with two stops in each.
Why it works
The lift's script only checks for the spanner the first time; it then sets the lift's flag and never asks again, so the spanner can be left behind.