Weird unidentified black thing stuck to my piggies behind

[Poorvi]

Hi guy, first off I'm from India and I've shown to 3-4 vets but none have an experience in Guinea pigs and are unable to provide anything, I would request you guys to maybe help me however you can.
So my guinea pig is now 5-6 years old (adopted so don't know the exact age), lately she was making some squeking sounds in the night, so I looked her over and there was some black stuff stuck to her behind, now I'm not sure if it's just pigmentation, but she squeled a bit when I was touching her around that area (also cause it's a sensitive area for piggies)
Please check the pictures in photobucket, link below any help would be amazing! Please please!
Thanks a ton

http://s1070.photobucket.com/user/poorv ... a/library/

[Lynx]

I am copying crops of a couple of your pictures to display here (let me know if that is okay):






I believe this is simply a dirty grease gland. If you can get some cold pressed coconut oil (or baby oil if none is available), you can apply some to soften it and gently clean off with a detergent.
grooming.html#grease_gland

[Poorvi]

Thanks a lot for replying, I tried cleaning with soap water, but it's still the same, and she does have a habit of biting this place, I was checking guinea lynx and I came across a skin tumor sort of thing that looks exactly the same, it's stuck to the skin, but I can try some coconut oil too
And thanks for posting my pictures! That works like a charm :)

[Lynx]

Soap water alone often does not work because it is so greasy and hardened. Hopefully it will soften for you with the coconut oil and I will be right that it's only a dirty grease gland.

[Poorvi]

The coconut oil seemed to work to an extent, there was some black grease/dirt that was stuck to part of the hair which I clipped off but I do see some pigmentation underneath though I've not clipped everything off yet
Should I do it over a span of 2-3 days, soften the area with cocount oil and then cut the hair off because she squels a lot when I touch that area

[Lynx]

I do not think this is an emergency to if you'd like to take your time and make it less painful, go ahead and do that.