Leaking rear brake DIY job or mechanic job, I have some skills.
rear brake leaking, Is it a DIY job on 1990 Geo Prizm
Drum? If so check your wheel cyclinder, it can be a DIY but follow the repair guide from chiltons and you'd be able to. If it's the brake line still could be a DIY, just a wee bit easier, personally I'd say give it a go, save yourself a ton of money if its the wheel cyclinder it'll be about 10 bucks for the part prob 35-45 min to pull and put it on
If it is a rusted brake line, I'd take to a mechanic.