These 'O' ring piston upgrades are only available from Dream Steam, and are provided with instructions. I have no experience with the Dream Steam ones, only the earlier IP Eng & Mike Chaney ones.
They are a development of the original IP Eng 'O' ring piston upgrades which were covered in this thread -
http://gardenrails.myfreeforum.org/ftop ... -asc-0.php
Only relevant photo I have is a completely disassembled Mamod Cylinder & Piston assembly.
When you go to take apart the cylinder assembly rest the saddle of the cylinder on a hard surface (e.g. jaw of a vice) so that the end cap will come off easily (make sure it has something soft to land on just in case you need to use it again).
Getting the brass big end off the piston rod is a little tricky. Secret is to make sure you hold the piston rod securely but without damaging it - that is no mole grips unless you are happy to scrap the piston rod - try using a piece of leather or similar wrapped round the piston rod and clamp it in a vice.
If your cylinder assemblies were fitted with the old Mamod gaskets then these will need replacing as they generally disintegrate upon removal - if it is fitted with the later MSS gaskets careful prising off with a blunt edge may be successful.
After fitting it is recommended to use the original Mamod pivot springs until you have the new assembly run in. Also you will find that unless the steam oil has been thinned due to heat that these pistons will be very stiff to move - when I fitted the IP Eng upgrades I flooded the cylinders with lots of light oil (3 in 1 or similar - do not use WD40 as it eats 'O' rings for breakfast) which helped the running in process until the steam oil would flow properly. These 'O' rings need regular lubricating - use of your dead leg lubricator has been covered in the other topic.
Chris Cairns.