I've never heard of any function problems with the early guns. Collectibility-wise, the earliest Mini-30's are scarce.
They had a 186- prefix instead of the regular run with 189- serial number prefixes.
The 186- guns had a plastic "Sporter" style buttplate instead of the curved Mini-14 style carbine buttplate. Early Mini-30's also had Mini-14 marked magazines.
The earliest Mini-30's are known in the sn range of 186-00514 to 186-02174, and one of this configuration has also shown up early in the 189- prefix (189-01047). There probably weren't over 2,000 made.
SN's 186-00001 to 186-00500 were not produced.
Chet15