944 leaking antifreeze, transmission sound

[q944]

I have an 83 NA 944 (stick), and am having a few issues with it. First of all the antifreeze has been leaking out from under the radiator, even after I tried to use that antifreeze sealing liquid crap that you pour in your radiator. The other thing is that whenever I shift gears(unless perfectly smooth), the car makes a clunking sound. When I let off the gas fast the car jerks forward and back(which may be normal- the other old 944 i drove did this). Also is anyone here from the twin cities(MN)?Any help or tips would be greatly appreciated. Thanks