[cerial]

The vent tube(check valve) on your th350 is 8-10" above the gear selector seal.

Should be able to run your paw up there and feel it.

If you remove the driveshaft(s) and lower the cross member you can drop the transmission enough to install a tube or replace the check valve. Pull your distributor cap also just to be safe.

Some shops will paint right over the thing or never replace it.

If the thing is 2wd a check valve is alright to run. If 4wd a tube going up the bell and to the firewall will avoid you thinking about another rebuild when you have a water/mud slurry seeping into the cab.