Help & advice needed - Vivitar S1 35-85mm f2.8

[DigiChromeEd]

I bought a Vivitar Series 1 35-85mm f2.8 recently in absolute mint condition cosmetically c/w original caps etc. Unfortunately the focusing ring is stuck solid. The zooming function is fine as is the aperture control. The lens shows no sign of damage.
Has anyone come across this fault before with this lens and is it something that can be fixed relatively easily? I could return the lens for a full refund but am loathe to do so as it is in mint condition otherwise.

[Gardener]

Here the service manual http://www.boggys.co.uk/page13.html but I imagine it's a total PITA to fix.

[Lloydy]

I had a Tamron 28-135 that jammed solid, no amount of brute force would give the slightest movement of the sleeve. I tried to dismantle it, but the sleeve needed to move to get at the screws to get it apart. In the end I took a hacksaw to it just to find out what had failed to make it so solid, and I found that one tiny plastic roller that moved in a curved slot and it's screw had come off and gone between the two main rotating / sliding parts. There was no possible way to get that lens apart while still jammed solid.

[Gardener]

This one has a focusing helicoid so it's probably congealed grease. I once had a Nikkor 105/2.5 like that. It took a month of soaking to break it apart.

[DigiChromeEd]

OK everyone, thank you. It's going back to the seller tomorrow.