Check the level comparison boundary

A visual gauge may have limited resolution, and levels can depend on temperature, equipment position and operating state. A small loss may be difficult to distinguish from those changes. The same indicated level on two dates therefore does not establish zero loss. Conversely, a changed level does not identify the external stain as its cause unless the fluid path and timing support that connection.

Investigate the stain independently

Compare a stable old film with a newly wet boundary or expanding patch under comparable observations. Maintenance spills, oil transported by airflow and runoff from another component can resemble leakage. Approved cleaning may help a qualified investigation, but should not erase needed source evidence. Do not search for a pressurized leak with hands or loosen a connection to see whether fluid is present.

A gauge read before and after a change in temperature may be a poor comparison even when the marks are easily visible. The reviewer should identify comparable states before using an unchanged level as evidence against the independent report of recurring fresh fluid.

Ask a source-and-quantity question

The service specialist should identify what evidence can locate the source and whether the relevant function is affected. Acceptable seepage, where specifically documented, cannot be inferred from a general reservoir appearance. No MARSTON fluid circuit, allowable loss or sight-gauge accuracy is assumed. The practical decision is whether the stain represents an active condition needing action, with the result based on the installed component instructions.