Coolant Smell but no visible leak

So this car has a smell of coolant leak but there is no visible leak found. Last checked the coolant level was down quite a bit confirming a leak. I filled the coolant and a few days later checked and the level and it was not down by much but still the coolant smell. This car has had the bypass fixed before but not replaced with the aluminum versions. I am thinking this is the issue but not sure so seeking additional thoughts.