You can buy service kits from the US for hydramatics. They were referred to as the Slim Jim box, with the EK's using the Model 5. You can get the service kits from eBay for the Model 10, and suspect they fit Model 5...
https://www.ebay.com.au/itm/ROTO-10-SLI ... SwHnFVtY58... but the prices are horrible. Some places (from memory Repco) were also importing them, though selling at a similar price. I imported a box of 50 filters a few years back, and sold them off at cost. It was about $70 each for the filter, gasket and o-ring. Sadly I don't have any left other than the ones I gave Dad for the EH Prem.
Cheers,
Harv