Millimeter wave (mmWave) imaging has promising potential for many applications because of its fine resolution, object-penetration capabilities, and all-weather, all-day working conditions. Combined with low-cost mmWave radars, the synthetic aperture radar (SAR) technique enables flexible, cost-effective, mmWave imaging solutions. This paper experimentally investigates how SAR imaging quality depends on in-aperture 2D Gaussian position errors. We emulate a wide range of position errors with root-mean-square values ranging from 1 mm up to 256 mm, covering between a fraction and a few tens of the wavelengths at 77 GHz. The presented results provide useful guidance for designing portable mmWave SAR systems that can benefit from flexible and low-cost motion tracking solutions. The data and code are publically shared at https://github.com/radar-lab/SAR.git.