Volvo Repair: 99 Volvo s70 AWD, home handyman, volvo s70

Question
I detect an aroma that has to be antifreeze in the car.  There is no loss of fluid in the reservoir, so it must be a very minor leak.  (Are the fumes toxic...?)  Would it be hoses?.. or the heater core?  What would you suspect?  It does make itself known in the cab even if the air and heat are not on.  Could I drain and flush and replace with clear water?  That might risk other harms ike overheating and freezing, I guess.  I have seen cores for $120 to $320.  Hoses I don't know.  Can this be done by the mid-level home handyman...?

Answer
it is fairly easy to replace the heater core which is what it sounds like the problem is.I would purchase a repair manual to help in replacing it but it is easy.it coumes out a access spot on the drivers side under the dash board.the gas pedal will need removed to replace it.