I do believe the situation you are pointing to has subsequently been dealt with. More recently (like since 1984) OMB has cheated postal retirees out of tens of billions of dollars by overcharging for retirement.
Now, going directly to the health insurance situation, the federales forced postal employees into Medicare and that smarmed up what or where subsidies might have occurred.
Irrespective of that I kept close track of every penny I paid to retirement and determined that if it were simply routed into T-bills I would have paid for all of my possible retirement costs FOREVER.
Most people simply don't realize federal employees under the old CSRS system paid for their own retirement.