Here's a technical analysis of the Sturmey 5:
https://forum.cyclinguk.org/viewtopic.php?f=5&t=128331
The hubshell contains a drum brake. Don't fit an oil port. Use NLGI 00 grease on the internal gear mech as the factory did, and do the bearings and labyrinth seals with Sta-Lube blue marine grease.