no reason you should have scar tissue...I have been using the same 4 sites for almost 10 years and I do compete so ed injections have been done, eod is what i normally do and no issues. How much are you injecting into each site and how often are you hitting them?
ED, typically 2-3CC's water based peptides, i try to rotate but i only have slin pins (waiting on a shipment of 10cc luer lok types so i can minimize injections), i reused a few of them so the tips probably got blunted and tore into the muscle a bit, i think my technique wasn't the best, needle kinda wiggles around a bit, i'm getting better results now that im more skilled at shooting.
the worst site was the outer calf, i think i got an abscess because i pulled a valentino and shot with a dirty needle, it was red and itchy for a while, was stupid of me i didn't think anything of it at the time though. now it just feels kind of hard, and when i shot again the needle "crunched" through and it bled for a bit, needless to say im avoiding that site for now.
i read that oil-based gear almost always causes a sterile abscess unless you inject it super slowly (i believe 3 minutes per cc was the safe speed), which causes scarring as well.
i'm just starting out with injections and am probably going to be using all kinds of drugs for a long time so i figured scar tissue buildup would be inevitable at some point.