Cichlid gone mad!

A few months ago I inherited a 42gal tank that a friend did not want any more. It came with a large pleco and the craziest Labidochromis caeruleus I have ever seen. The lab is a 4 year old male who seems to have episodes where he just goes nuts! He thrashes about and especially likes the bang himself upon the heating tube. He always has some kind of sores/wounds all over. Right now he even has a small hole in his tailfin and a gash on his side (pic attached). The wounds always heal and over all he is a very friendly little guy.

I wonder if he thrashes around on the tube because he sees his reflection is perhaps is just really bored. Perhaps he just likes it cold and hates the heat! OK, I know that is unlikely.
Anyway, I really like this little guy and hate to see him constantly hurting himself.

If anyone has seen behavior like this or has any suggestions as to what I should do please let me know!

Also, I have been wanting to add more mnubas to the tank however I have gotten many mixed warning against this from the local fish stores. A lot say that since this fish has been an only fish for quite a long time (perhaps up to a year), that no other fish would ever be tolerated, and he probably is the lone survivor (there used to be at least 8 fish years ago) because he is the aggressive one. He never seems to bother the pleco, actually often times he is just lying around right beside him. Once again, if you have any suggestions I'm open to them! Thanks.

Hmm, didn't think about the pleco getting at him. I'm not sure about that one though, he gets sores like this all over and in very random sizes (usually tail and sides right where he rests in the rocks). They sometimes start smaller and get larger as I think he rubs on the rocks some, maybe to scratch the irritation. I add stress coat to the water to help some.
I'll watch the pleco more to see any signs of bugging my Lab. Usually the pleco just sticks with sucking his favorite rocks and seems content with that. He is a pretty large guy too, I think his mouth is actually quite a bit larger than the sore. <shrug>

Heh, perhaps. I'm just afraid that he won't tollerate any other fish. I guess eventually there is only one way to find out. Just get some and see what happens?!

I am just going to watch my yellow lab and let him be crazy I guess.
As to my question about adding other fish to the tank, any suggestions?
What are some other fairly non-aggressive cichlids or other fish that would be potentially compatible. I hate for the whole tank (42-46? not sure...bowfront) to be for just 2 fish (lab and pleco).
And any suggestions as to do I need to take the lab out when I add new ones and add him a few hours later? Someone else told me once that I should rearrange the rocks and then add the new fish? I do not want the little guy to lose his favorite spot, but I don't want him to be alone either, or destroy any new guys.
Please let me know what you think! Thanks =)