Anyone else see gradual RT creep after replacing UHPLC pump heads? Over five days my caffeine standard shifted 3.2 to 4.0 min on a C18 with 60:40 ACN:H2O + 0.1% FA at [redacted]/min, 30 C; pressure is stable but baseline noise is up about 10%, so I’m weighing proportioning valve calibration vs degasser efficiency vs solvent lot — what would you probe first?