Synchros stuck in Geo Metro 5-speed manual trans

[buggywhip]

I have a 1991 Geo Metro that was in storage for 7 years. The 5-speed manual trans was fine before that, but now I can't downshift to 1st or 2nd without stopping or double-clutching, since the 1st and 2nd gear synchros aren't doing their job. Downshifts to 3rd and 4th work fine.

I envision the car sitting for 7 years and the the oil forming varnish or sludge and binding things up. Is that possible? If so, is it realistic to suppose that a solvent or additive could break this up, and if so, what would it be?

I was told by a mechanic they could be freed up by removing pan and moving them around by hand, but am hoping to avoid this, also wondering if anyone has tried this.

Also, have a used trans but know nothing of its history. Is there a way to check its functions before I go to the trouble of installing it?

[Isuzuzuki man]

Change the fluid, use some good fluid like Redline MTL or equiv.