All overdrive transmissions will hold in reverse when parked with the OD engaged. That is not the issue. The reverse lock out is designed to prevent the overdrive from engaging in reverse when driving. If you look at the overdrive shifter shaft, it has dual components, one part manually engages/disengages the planetary actuated with the cable, the other component disengages the planetary with a cam assembly on the reverse shift lever internally. The reverse shift lever on a 4 speed may not be in the correct position to perform this function.
Fred
