I did a lot of reading online after I bought my K100 MK7 on an impulse last June (another Dlask clearance sale as the MK12's were coming). I didn't really come across much in the way of reliability concerns or negative comments. Where do you get the "spotty reliability record"?
My guess is from the Mk6 guns produced prior to 2010.
There were problems with cracked grips. The cause was often due to mishandling. Some users were trying to take the gun down by pulling the trigger guard straight down, rather than forward and then down. This stressed the ridge that the trigger guard locked into. Similarly, if users shot the gun with the trigger guard unlocked, the grips could be cracked as the trigger guard served as a shock buffer. With it in the wrong position, the slide in recoil would hit it early and in the wrong position.
The Mk7 grip strengthened this area and changed the trigger guard shape to help avoid user induced problems. When we introduced the .40/10mm/45 grip the locking lever system was adopted to eliminate to area of concern.
The early Mk6 guns still used an investment cast slide that was finish machined by CNC. While it was easy to spot external pores and scrap the pre-form, some internal voids might not be spotted even after machining. After some cracked slides, Jaroslav pulled the pin on using any castings and went to 100% CNC'd parts.
When STI were importing the K100 and P1 as rebranded GP6 and GP5's, they wanted to have a hammer profile that looked more like a STI product.
They supplied wire EDM hammers for those guns. Unfortunately the steel used for the first batch was overly hard and not ductile enough, and they suffered premature failures.
STI changed the type of steel used the second version ran fine.
The most recent issue was limited to a shipment of guns that went to the US via Century Arms in January 2013.
Two customers suffered barrel ruptures that didn't seem to be related to bad ammo.
When we investigated, it looked like the cause was the chemical makeup of the steel was not what the lab certification said.
The % of sulphur was higher than permitted in those barrels.
While it was likely limited to only a few of the raw barrel blanks we purchased from one of Europe's largest barrel makers, we recalled and replaced every barrel in that shipment.
It also accelerated our plans to bring barrel blank production in house.