Engine check light- radiator leaking?

[Lordblood]

My engine check light came on today, bad luck . Before I take it to the mechanic (he's asking for 90 dollars to get it diagnosed) I had a look around to see if I could spot the problem. Seems like the radiator is leaking, I filled her up full with coolant about 3 weeks ago, and today I check to see that it is near the minimum mark.

Now, first off, can I use a sealant and pour that in to stop the leak? Or do I have to get a new radiator altogether. And also, if I do need to get a new radiator would it be wise to get a 90k service and new clutch done at the same time?