Update
Ministry of Land, Infrastructure and Transport of Japan has made an announcement regarding JAS MD-81/87 engine incident. The announcement indicated that only those engines which received a maintenance repair on stator fins showed cracks on stator fins.
Stator fins are welded onto a metal plate in a compressor. However, on JT8D-217A/C engines it is possible to develop a gap between a metal plate and a stator fin after about four years of use. The manual written by Pratt & Whitney indicates that a stator fin parts to be replaced with a new one or repaired after certain time interval. JAS contracts this specific stator fin maintenance to a subsidiary company of Pratt & Whitney in Singapore.
The investigation so far showed that only those engines which received a stator fin maintenance at Singapore showed cracks on a stator fin.