Out of the 30+ used cars I've owned (mostly japanese) never had any I considered unrealiable but have had some bad luck with a few.
87 Toyota MR2 Automatic GT (rare) trans went out at 55K miles a month after I bought it. Had it rebuilt a month later the engine blew up so I swapped it out and it ran with no issues for the next 4 years.
2000 Tundra trans started slipping at 58K miles.
97 Del Sol AC compressor went out at 37K miles dealer wouldn't fix it under warranty so I got pissed and traded it.
Surprisingly out of all the nice cars the most reliable was a 2004 Saturn SC1 with 85HP. Hated the car but beat the living crap out of that car for over 100K miles and other than using oil on a regular basis it was indestructible. Even ran it into several guard rails and 2 trees finally to create enough damage to total it out so I could claim my gap insurance to cover the extra costs of shady used car sales.
2008 135i - MHD/JB4, MS DP's, AMS IC, UI CAI, CDV delete, M3 control arms/Links, RE Toe Link, ECS Trailing Arm, M3 rear SF & Trans bushings, SS brake lines, Michelin PSS.