Never ran as the 557, for a while that was used on number 57s that was extended from Heworth to South Shields after South Shields depot closed (https://www.flickr.com/photos/gjm-photog...4178710837), though the 558 would eventually replace the section of the 557 from Boldon School to Heworth Interchange.

For a while in the early noughties, the 558 only ran on Sundays between Heworth and Seaburn operated by Jayline using various Mercedes Minibuses and Dennis Dart SLF / Plaxton MPD (sadly before I had a decent camera). As on Monday to Saturday daytimes, Go North East operated the X97 which ran from Newcastle to Seaburn. (Back then the 558 ran via the dual carriageway from Heworth to Testos and didn't bother with Fellgate Estate.) This all changed when the Metro was extended to Sunderland. The X97 bit the dust and was kind of partly replaced briefly by the X98 which went from Boldon to Southwick via Downhill and Red House Estate. The 558 then went to daily operation between Seaburn Dene Estate and Boldon Asda, though I think it was extended to do a loop around the Cotswold Estate. After Jayline it was operated by Stanley, then Redby got the contract usually using a Merc at first before going Low Floor with Darts or Solos, at one point Redby also ran the school run on the 558.

Stagecoach may have ran the long one briefly around 2002/2003 before the contract passed to Stanley Travel, but prob didn't use the 04 plated Darts.

Classic ran a weird variation known as the 559 - https://www.flickr.com/photos/gjm-photog...0932321736

Operators I've managed to photograph on the normal 558 with my camera are....
Compass Community Transport - https://www.flickr.com/photos/gjm-photog...2987518893
Gateshead Central - https://www.flickr.com/photos/gjm-photog...6544670559
Go North East - https://www.flickr.com/photos/gjm-photog...1142403582
Northstar - https://www.flickr.com/photos/gjm-photog...5408118780
Redby - https://www.flickr.com/photos/gjm-photog...9424322247
Stanley Travel - https://www.flickr.com/photos/gjm-photog...2791528258
Veolia Durham - https://www.flickr.com/photos/gjm-photog...0612629863