Additional evidence of Syrian Su-24s being upgraded in Rzhev has come available. Ironically, the evidence was published on the 514 ARZ aircraft repair plant's own website. This plant is responsible for upgrading the planes from MK to M2 standard. More details about the Syrian Su-24s undergoing this upgrade can be found here.
The photo seen above shows personnel of the 514 ARZ plant working on Su-24 serial 3506. Su-24 3506 is one of the twenty-one Syrian Su-24MKs being upgraded by the repair plant in Rzhev.
514 ARZ also removed the direct link. (13-1-2014)
Yet, the author still has printscreens of the site while showing the Syrian Su-24.
Syria's recently upgraded Su-24s (1)