searched all over forums and could not find distinctive answer... I suppose it must be heater core but thought that would be leaking on passenger side? Any suggestions?

 

Could just be one of the hoses also.

 

94 4Runner 3Vze 200,000+

 

I don't know if it's the same on all yota models but in my 90 there's a small box I have no idea what it's for but it's right on the firewall and it's for coolant. If there's a leak somewhere around that it would endup on your mat in the cab. check that out.