possibly during the last T-belt replacement the bolt wasn't set to high enough torque and it just came loose.
They have a revised bolt that fits the 12 valve...
And they have a rivised bolt that fits the 24 v 3.0 / and 3.5., I reconn they could all have this problem. The recall had the Montero Sports in it but I don't remember if it included the SOHC 3.5. I'll go on AllDatapro and see if you want.

dave h.
'89 Raider V6 5spd;Aisin Hubs;; Gen2 LS: frt. brakes, rear coils;U.C.arms;R.trailing arms;idler arm; rear LSD axle w.disc brakes ;2 battery system for Dog's fan; relocated ECU; custom bumpers;J.Baker receiver;Conferr roofrack; t-bar crank.