The PRHT's Achilles heel is its soft sector gear mechanism, which requires regular greasing to survive past ~50k miles and, when it fails, can cause collateral damage to the retraction assembly. The gears are no longer available in the USA and few independent Miata mechanics know how to service them.
PRHT sector gears wear and are NLA in the USA
Mazda MX-5 Miata (NC) · mechanical