Warn nylon fittings on the shift fork, allowing the ring to partally engauge?
How quickly is this happening? Those Ford lockouts are famous for sticking. Could it be a Sharp edge "sawing" at the strap? Spool limited or open? I could look
but my internet is slow. You need any 231/233 parts I have em.
Edit: fluid viscosity or lose engaugement ring I see you have a spool. BTW I have 2 shrot side and one long side f150 shaft for you
can't find any good stubs.