'the sun is slightly too round to agree with our understanding of its rotation'
The above article covers recent space based observations of the shape of the sun. Any large spinning object tends to bulge out at its equator, the earth's equatorial diameter for example exceeds its polar diameter by about 13 miles.
The sun seems to have less of an equatorial bulge than we would expect from basic theory.
This may actually offer supporting evidence for Vorticitating Hypersphere Cosmology which predicts a general fillip to orbital velocity of
Vo = (Gm/r - rA)^1/2
Where A = Anderson decelleration.
This has the same effect as an increase in 'centripetal force' at large distances and could well lead to less oblateness in stellar sized rotating bodies.