I was having a similar problem when DD was quite young, cracked nipples at the base, painful feeding. The LC said - as the others have pointed out - that my DD was only getting the nipple in her mouth and not enough breast. The LC gave me a really good technique for getting her to get more breast in her mouth, I will try to describe it but it is a bit hard to convey it clearly in writing.

Basically my LC said that the nipple really needs to be hitting the roof of the babies mouth so that it is drawn right in to the back of the throat when she starts sucking. To get this to happen, as DD was opening her mouth to attach, I put one finger on the breast on the 'outside' of the nipple (so a few centimeters towards my elbow or ribs) and applied enough pressure to make the nipple point out (towards the armpit or ribs). This meant the nipple was going into her mouth pointing towards the roof of her mouth instead of pointing directly into her mouth/down her throat. I am not sure how you would replicate this position/angle using Baby Led Attachment, but this technique REALLY helped me out, I hope I have worded it so it makes some sense!

That fixed our attachment so it didn't get any worse or create any new cracks, but it didn't help to heal the crack that was already there. The best thing I found for this was a bit of breast milk put onto the nipple and left to air dry. I also used a nipple shield for maybe 2 feeds. This didn't actually stop it from hurting during the feed, but it did give my nipples a few hours break from that direct contact and gave them time to heal a bit.