Oil Seepage on 308 Oil Cooler Fitting where hose goes into fitting how to fix

I bought a new oil cooler for my 308 and there is a slight seepage of oil coming from behind the fitting. Right where the hose/flare fitting goes it. I have tried to tighten them more but that is about as tight as I feel they should be. Is there anything to stop this? It is bad but after a drive if you wipe your finger on the joint that goes into the fitting I can see a small smear of fresh oil on my finger. Any info would be appreciated. Thanks.

I'm not exactly sure where you have the leak from your description. However, if it's from the threaded area where the hose meets the cooler fitting ( and there are no imperfections in the mating surfaces), perhaps you could try to reinstall using some teflon thread tape to make for a tighter fit.
If it leaks from the cooler itself, a radiator shop could likely diagnose / fix it fairly easily. Or, if it's new and the fault is in the cooler, send it back to the supplier to swap for a good one.

Finally, I don't know if all 308 coolers/ lines are exactly the same. I know they charge different amounts for diffrent models' oil lines. Could it be that there is some mismatch here between the cooler you bought and your existing hoses?

Yes it is hard to describe. It isn't from the cooler. It isn't from the threaded part of the fitting but from the flared end that goes to meet with the cooler. Basically, the female nut can slide over the hose with the flared end. The flared end goes into the oil cooler where a female (lack of a better term) flared end is present. After it is tigthened etc. a slight oil seepage can be noticed coming out of the pipe/hose that goes through the male nut. The seepage is in front of the fittings toward the hose. In other terms oil is getting around the flared fitting and coming out from behind the male nut where the hose goes through it. It is such a slight amount it may not be worth pursuing until it has had time to settle. Right now after a 20 min. drive I can wipe my finger on the back of the nut and get a slight smear of oil. I would estimate 1/8th of a drop max. Thanks.