I'd say that an overall inspection of the wiring for the blinkers is in order.
I had trouble with the ground conductors for the taillights corroding in two
on my 73 164. I ended up soldering in pieces of copper wire to replace
them. It was hard because I was on the road in the US and lived in Panama
at the time. Whenever you get problems with rain that you don't get in
dry weather, look for wet stuff, especially if any kind of salt (sea, road,
ice cream, fertilizer, etc) might be involved.
If you have fender-mounted blinkers you should certainly look at them.
Volvo light sockets in general are problem areas. For some reason European
electrical conductors tend to develop a transparent, nonconductive film over
time. About all you can do is scrape all contacts till they are shiny.
Socket shells and the cylindrical portions of bulbs are especially bad
about this.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma