My waterheater has a slow drip from the drain line and the water is slightly warmer then tap water. Is this caused by a leak somewere else in the tank and this is the only way out? or is it the water cooled so much before it drips out that it is slightly warmer then tap water and is it easy to just replace the drain valve?

Are you referring to the drain tap at the bottom of the water heater, that drips?
Easy fix is just to get a brass screw on hose end with a rubber or vinyl washer in it and screw it on. No drips.

OTOH, if this is a drip from the pop-off valve then that valve likely needs to be replaced. You can try just opening the valve slightly and letting it spring back closed. This could clear any mineral deposits that may be on the seal inside. Doing this will work about 25% of the time. If it still leaks, then it's time to replace the pop-off valve. Under a $10 part at home stores.

I cant answer where the water is coming from
could be a couple of places. only you can figure out where
by looking at all conections and plugs
look on the top of heater, at the water connections
are they dry? any rust on the pipes?
look at the pop off. any sign of water?
at the drain...stick your finger up around the drain connection, can you feel wet insulation?
look at where the drin pipe hooks into tank. any water or rust?
water in tank is always hotter by a few degrees than water coming out of tank.
i dont know why, its a physics thing. above my pay grade!!!
I personnaly, am against tripping the popoff
because they ALWAYS dribble afterwards. then i gotta hit them with my plyers, to make them stop. to me...a popoff is to be left alone,
that is debated among plumbers, after work at the watering hole. some say popit. others say leave it
i have found that the repair guys say popit, cause then..they can charge to replace it. LOL
me, i'm construction. i try to avoid making work for myself.LOL

We never worry about tripping the pop off valve. As posted they may leak after doing that and yes a tap or two may correct the culprit properly. If not time for a new pop off valve. You really don't have much to loss @ that point.