This article presents a Monte Carlo-based analysis of the effects that random manufacturing errors produce on the radiation diagram of resonant slotted waveguide linear antennas. Positional and dimensional errors on the slots are considered. The study is performed using a tool implemented in MATLAB based on the Taylor synthesis of antenna parameters and the analysis of arrays and aperture models. The tool assesses the impact of the different errors on the radiation pattern. The results show that slot dimension errors have a dominant effect on the pattern over the variation on the slot position in the waveguide. A prototype of the studied antenna was build and its radiation pattern measured against the predicted mean and extreme tolerance margins. The results obtained are satisfactory, thus validating the implemented tool.