Sterling Rear Panel Split

Tractorbob3

I have a 2008 Sterling Eccles Jewel in good overall condition.  However, I have found a 75 mm split in the rear panel running from, and at right angles to, the roof seam, about 25 mm in from the nearside edge.

Some friends have the same make/model/year and - guess what - they have discovered their unit has exactly the same fault.  The split looks like the panel has just pulled apart - there is no sign of impact damage.

So I am now wondering if this is a coincidence or a known fault - and what is the best cure?