Thanks Zeracer. The only hose clamps I see are on a short pipe connected to the reservoir. The connections are not oily or dirty. But the clamp screws still had a turn left in them, so they are now tighter. There's an oil and dirt smear on the underside of the reservoir, and hoses directly under it and the connection to the pump have damp-colour patches. That points to a possible leak from the seal, so I've ordered one. I guess when I remove the reservoir to replace the seal, I will get more of an idea about the possible source.