How should I pronounce "Worcestershire" as a rhotic English speaker?

Merriam-Webster (usually a good guide for rhotic US accents) gives \ˈwu̇s-tə(r)-ˌshir, -shər also -ˌshī(-ə)r\.  The OED doesn’t give a rhotic alternative at all, just /ˈwʊstəʃə(r)/.  Checking a few random other sources, I can’t find any suggesting that the first r should be pronounced.

I’d guess (fairly confidently) that a rhotic BrE speaker would say /ˈwʊstərʃər/ or /-ʃɪər/.  Using /-ʃaɪər/ (Merriam-Webster’s \-ˌshī(-ə)r\) for the suffix -shire is strongly marked as an Americanism, to my ear, though I don’t know a source to back this up.

I'm from Worcester, I was born in Worcester. Common Worcester is a hybrid dialect of rural West Country with a substantial hint of Brummie/Black Country. Locals including myself naturally exaggerate R's or include invisible R's at the end of many words. The prenounciation for locals and yourself should simply be 'Wuster'. (Wuss-ter) 'Wustershear'.

Easy. Simple as that.

The pronunciations reported by the NOAD are /ˈwʊstərʃɪ(ə)r/, /ˈwʊstərʃaɪ(ə)r/. Having a friend who lives on Long Islang, I am used to the first pronunciation.

I don't remember my phonetic symbols brilliantly so I'll try this (mostly) without - as a native Briton I can tell you it's (roughly)

Woostəshə

(the "oo" being that of "look" not "food" or "zoo")

or, less commonly, just "Woostə"

That is, in the local accent. I can't speak for the whole of Britain.