Oil pressure guage

[Ladybird]

After working without problem for the past year our oil pressure guage has begun 'sticking' for several minutes before acting normally, smacking across to full scale and then settling to 5/7psi for normal running  There are no obvious leaks, actual pressure is normal it just seems to be a sticky guage.  There doesn't appear to be any interference between needle and the face of the guage. Is this a common problem?  Can it be fixed?  Any advice welcome.

[squeak]

Possibly a bubble in the oil line, could try slackening the feed at the gauge, wrapping the joint in a rag, start up and when the rag is oily switch off and tighten.