Woke up this morning to find some coolant below front of car, not too much but fresh coolant drops sticking to lower air dam/guide/shroud ... coolant level looked good.

I peered around the radiator and only saw some wet spots on the left side mid-way down the radiator - i can't see much else with all the clutter in there.

What should i inspect, look for?

Take off the air dam for a few days so you will know exactly where the drips are coming from. Examine closely the two large radiator hoses, top and bottom for leaks, I use a paper towel rubbed on the hoses. When the engine is warm, use a flashlight and look for steam or fresh antifreeze on the cooling fins - front and back sides. Might have been a rock from a "sand" truck.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)

So after observing this leak for a couple of days its very similar to many other radiator leaks that have been posted

http://www.brickboard.com/AWD/index.htm?id=142028

i.e. occurs on drivers side, coolant seen going down fins on drivers side, only occurs when outside air temp is cool, seems to be coming from where hose 'meet' radiator and ofcourse there is very 'little' coolant leaking everytime this occurs

i figure i'll use Prestone Stop Leak - however the product says to put it directly into the radiator -- i could be wrong but i don;t think volvo radiators have direct inputs - normally has to be put through coolant reservoir right?

You could stop at a radiator shop and have them do a pressure test. You are correct, there is no radiator cap.
BTW, my V70 just had a burp of antifreeze on the garage floor. So I am about to remove the splash guard to help me locate the source when it does it again.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)

so i started pressing on the hoses whilst the car was warm and i can clealy see tiny bubbles + fluid seeping out of an area on the top passenger side of the radiator where it seems like the two tanks are pressed together by a metal seal .. it is this from this seal where things seem leaky.

So the question is .. should i replace whole thing or use Prestone Stop Leak first? Will Stop Leak clog anything else you think?

Ouch! Stop Leak additives are intended for tiny pinhole leaks, not large leaks like you have.
The dealer will only remove and replace for a small fortune. An indie will charge a lesser labor rate to R&R. A radiator repair place will remove and fix the radiator, if possible. You found the leak, so you won't need a pressure test! I would ask around at some radiator shops and see what they say. Be sure to ask about the amount of time involved.
If you feel comfortable with doing the labor yourself, ask them about the cost of doing a weld. Remember, your oil cooler, tranny cooler, and inter cooler for the turbo are all in there too.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)