Drive and reverse works but manual mode doesn't

[magpie #2]

I have a 1994 Subaru legacy non turbo non four wheel drive. Drive and reverse works fine but the gearshift won't let me shift to manual 3-1 with and without pushing the button on the gearshift. Any suggestions as to what is causing this. I can drive it as is, but everything else on the car works and we have always kept it well maintained so we would like to fix it. From what I have read up on it is that it's not the transmission due to drive and reverse works fine.