1993 explorer manual no 3rd gear Help please

I have a 93 top loaded trans with no thied gear all other gears are fine but
third is an open hole is it possible that I may hve lost a pin holding a
fork or sonething like that?? One day I shifted into third and nothing was
there! I dont think its the gears as there was no warning no grinding no
metal in the sump!
any help would be great.
thanks
Phil


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