PPE Gasket Transmission - Transfer Case. Replacement gasket for the connection between an Allison transmission and a transfer case. This MP-15 gasket is made from material designed for heavy-duty applications including diesel engines, compressors and other hard working items. It has excellent low flange pressure sealability and bolt torque retention, which is engineer speak for “there won’t be any leaks after you muscle the trans/T-case back together if you use one of these.”