Hi... I got this cv joint from a junk yard, when I opened the box I noticed that the cap (?) of the inner part of it its lose... I wonder if is just a matter of put it in its place and thats it...

Also, it has some yellow grease on it, should I put more of the same (what kind?), or I can grease it with regular grease or no grease is needed...

That cap coming off is normal, no worries there. When you install it, that cap faces the front diff and gets pressed against it, so there is absolutely no chance of it coming loose once you've installed the axle on teh truck.

As for the grease, I'd be cleaning all that crap out and packing it with som fresh high temp stuff.

Who knows how long that stuff has been in there!

If the cap isn't seated tightly before you install it, the grease, when warmed up, will leak out, sort of like a very slow oil leak. It'll make a little bit of a mess on your driveway over time, so be sure to tap that cap back on well.

Thanx guys.... A sealant or loctite will do the job?

No, you don't need to seal it. Just tap it on with a mallet and make sure it's seated evenly. However, if the lip of the cover is bent, it won't seal properly. In that case, you could try smearing some silicone sealant around the edges to keep it clean.