Seroma treated with alcohol - side effects?

The firmness may be related to scar, or may even be related to inflammation from the alcohol.  Inflammation often feels firm, but if this is the case should soften as the weeks go on.  More importantly, if you have had the seroma treated multiple times, and he continues to reaccumulate, your surgeon may need to remove the fluid sac with a short and simple surgeryBest of luck!
Dr. SubbioBoard-Certified Plastic SurgeonNewtown Square/Philadelphia, PA

Tummy tuck surgery often results in tissue undermining and development of a potential space where seroma could develop. With intraoperative modifications to the tummy tuck operation significantly decrease fluid build up By maintaining Scarpa's Fascia  The internal lymphatic drainage system is maintained for the abdominal wall. This dramatically decreases the fluid production at the operative site and therefore reduces the incidence of seromas. Chromic seromas can be a very challenging situation to treat and in extreme cases will benefit from reoperative surgery. 

With the persistence of a seroma, one has to think about whether a pseudo-bursa has occurred. In this situation, scar tissue forms around the area of fluid in the pocket is lined with cells that actually produce fluid. Until this pocket with its inside layer is excised surgically, usually these aromas will persist. An ultrasound can readily discern whether there is a thick wall of scar tissue around the seroma cavity. Hope that's helpful.