If this is a valid medical condition we are talking about, then you might be able to use this:
03-07-88 MOU
Section 4. Handicapped and Disabled Carriers
A. A rural carrier employee who has been safely performing
rural carrier duties, despite a physical handicap, and
who would be prevented ,from safely operating an Employer
provided vehicle, will not be require to accept a
vehicle or OEMA unless the Employer offers to modify its
vehicle to accommodate the handicapped employee.
and there is this: (not sure if it's provisions were renewed)
The second MOU, 'Waiver of Right-Hand Drive Vehicles Provided by the
USPS", was executed in concert with the 1993-1995 USPS/NRLCA National
Agreement. This agreement allows a regular carrier who had recently
purchased a right hand drive vehicle to request a waiver from placement of a
USPS vehicle, effective for two years from the date of the actual purchase.
Carriers who purchased right-hand drives prior to the May 1, 1993 effective
date of the National Agreement were also permitted to request waivers.
These waivers were to have been requested by June 25, 1993. However,
because this MOU has had a limited dissemination, there was concern that
some carriers and/or managers may not have been aware of its availability
and application.
Recognizing this limitation, managers may accept requests for waiver from
placement of an LLV from caniers who have purchased a right-hand drive
vehicle within the last two years. These waivers may be accepted until
September 30, 1993. In accordance with the MOU, proof of the right-hand
drive purchase date must be provided and tile waiver is valid for two years
from that purchase date. Managers and DJSC members should contact all
offices and alert them to the availability of this waiver request and the
September 30 deadline. After September 30, any carrier who is notified that
the USPS intends to provide a vehicle for his or her route may not request a
waiver for a prior right-hand drive purchase.
Rural carriers should be advised to contact the DJSC and/or district rural
delivery staff if they are considering purchasing a right-hand drive vehicle, to
determine whether their routes have been identified for potential vehicle
placements. A form for recording a carrier's inquiry and management's
response is included with the "Waiver of Right-Hand Drive Vehicles Provided
by the USPS" MOU.