Looking around the site, it seems that there's no single spot for external LED bulb upgrades - there's posts going back to 2008 on upgrades but nothing regarding LEDs in the tech manual.
If anyone has any more up to date/LED info that can be added to the below, please post copy/paste the relevant line and upgrades they've used. Any other modifications that might be required (eg relays) would be useful. As Jameshoward says, this increasingly a matter of safety (and not getting our valuable cars shunted)
Fronts (euro) - from tech manual
The main Headlight bulb is a 40/45 watt non-halogen (Bilux) bulb that can be upgraded today. The correct replacement therefore carries the designation "Halogen BILUX-AS-HALOROAD R2 12V P45t" (available from Osram or Philips) and is a special 45/40 watt halogen substitue for greater light output and longer life. It's very similar to the regular (European) 60/55 watt H4 halogen bulbs but with a slightly lower output (barely visible) and with the correct P45t socket for the old-style mirrors used on the W113s. The bulb has three projecting connectors to fit the car’s internal connector.
The Parking Light is a miniature bayonet bulb T4W on a BA9s base. An upgrade is available as 3886X to give more light. Replacements include: 3893, 57, 57X, 1891, 1893, 1895, 78223.
The 18 Watt Turn Signal bulb can be upgraded to a P3497 higher intensity bulb.
The Fog Light bulb is a 35 watt bulb on a BA20s base.
The Night Light (Clearance) bulb is a 3 Watt bulb on a BA-15s base. An upgrade is available to a more modern R5W bulb.
Rears (230) - can anyone clarify if the holders are the same for the later cars? Tech Manual has both clusters and they look very different but no clarity on the actual bulbs/holders)
Brake light: 18W / Base: BA15s
Tail light: 4W / Base: BA9s
Parking/clearance light: 4W / Base: BA9s
Back-up light: 15W / Base: BA15s
Turn signal: 18W / Base: BA15s
Love the idea above of the LED strip for the tail light.