Following a regular schedule of maintenance (see the Owner's Manual and the Factory Service Manual) will help you find signs of impending problems which you can then fix before total failure. Don't ignore new sounds from the engine - check them out to see if a problem is developing. Brakes are a critical part of your bike - check them regularly. You can prevent many roadside failures by simply examining the bike regularly while still at home.

Over the course of many years, the following problems have been shown as 'common' for various reasons.¹⁾

Clutch Spring Plate Failure
The Spring Plate has caused untold headaches for many riders. When the rivets fail they get caught in between the friction & steel plates, causing the clutch to malfunction, damaging the plates & the clutch basket. This problem is best addressed before it happens. The XLForum did an ad hoc poll of those who have or have not had failures of their Spring Plate. The poll showed the rubbermount models (2004-later) failing at double the rate of the frame mount models (1986-2003). The reason for the failures is unknown (??? due to a change in design and/or material, from rider increased horsepower or from the way the rider uses the clutch. ???).
Described in the Sportsterpedia HERE

Loose Battery Cables
Whenever you have electrical issues, the first thing to do is check the battery cables and do the basic four voltage tests. Then check the various ground points & straps. A huge number of issues are caused by battery cable deterioration and/or loose connectors. The negative cable to the frame is especially critical. All Sportster models occasionally have trouble with the battery cables but it seems to be even more prevalent on the rubber-mounted engine models from 2004-up (since the motor moves more in relation to the frame).
Described in the Sportsterpedia HERE

1998-2003 Nosecone Ignition Failure
The 1998-2003 Non-Sport model used an integrated ICM on the Sensor Plate. These OEM modules had a high failure rate. The MoCo stopped providing replacement units as soon as they were allowed. The only choice for replacement is aftermarket versions (such as the Ultima version).
Ultima Described in the Sportsterpedia HERE

2007-2009 Electrical Fuse Box
The 2007-2009 model years have a significant history of corrosion and gunk collecting in the fuse/relay tray causing low-grade shorts and erratic electrical operation - This is especially problematic if the bike is left outside or operated in the rain. It's a good idea to check & thoroughly clean this tray at least every year (or 4 to 6 months if parked outside).
Described in the Sportsterpedia HERE

Oil Pump Drive Gear & Pump Upgrade

The drive gear failure a common failure in Sportsters, even when nothing gets into the pump to lock it up first. The teeth get sharp and then they break off. If something gets into the pump and locks it up, the teeth get ripped off the gear. It's cheap insurance, even if you only plan to visit 7,000 RPM instead of living there, especially if you are already in the cam chest to install other cams.
Drive Gear described in the Sportsterpedia HERE

In addition to the upgraded Drive Gear, there is also an upgrade of the entire Oil Pump (first installed on 07-later Sportsters). The internal Gerotor return & feed gears were altered to increase the scavaging capability, but note, the internal parts for the new pump design are not backward compatible to (cannot be installed in) the 98-06 pump design.
Oil Pump described in the Sportsterpedia HERE