[The Radium King]

i agree - simple and principle of occams razor - the most likely culprit is probably the culprit. in this case i would argue that:
(a) injector is as likely or more likely than lifter
(b) swapping injectors is less expensive, and as simple, as oil change (open engine, two bolts, two electrical connectors, swap two injectors)

otherwise, i'd note that oil was changed only 3k ago, so should still be well within useful life. further, an oil change, spin on filter, etc., are preventative maintenance designed to stop problems from happening, not repair, which is designed to fix problems. if a lifter is screwed so bad that the engine is coding, then repair, not prevention, is most likely required.