Brake problems on my new to me boat trailer keep snowballing… Started with new pads, then a caliper, then master cylinder, and most recently a brake line. The annoying part is I have to hunt and order everything and new issues show up after each part arrives. I’ve been working on this for weeks.
The master cylinder is discontinued but I got lucky and someone on Market Place an hour from me had a brand new actuator. I was switching the parts and sure enough, I wasn’t able to reuse the gasket.
Talked with etrailer today and they can’t get one nor do they have a similar one.

Chat GBT says I should use an EPDM material to make one. I’m finding sheets of it but not exactly sure of the pressure rating.
Old one kinda looks like a cork rubber gasket but I don’t think cork rubber is glycol resistant.

Can someone post a link to something that would work? All the google and Chat GBT info is overwhelming and I’d like to make sure to fix it right the first time. Greatly appreciated!

I found this within seconds using google. I do not have any working experience with this. Just providing very quick google search result. Please note, there seems to be two different ways EPDM is cured, so look into which is better. And yeh, appears both are available throughout the net in gasket sheets.

Here is excerpt from Google:
”
EPDM (Ethylene Propylene Diene Monomer) gasket sheets are considered the standard, superior choice for sealing applications involving glycol-based brake fluids (DOT 3, DOT 4, and DOT 5.1). They are widely used in automotive brake systems, master cylinder covers, and hydraulic systems due to their excellent compatibility with these fluids.

Key Characteristics of EPDM for Brake Fluid:

• Chemical Compatibility:EPDM resists swelling and degradation when exposed to glycol-based brake fluids, antifreeze, and water.
• Temperature Range:EPDM compounds typically operate well in temperatures ranging from -60°F to 300°F (-50°C to 150°C), making them suitable for the heat generated in braking systems.
• Limitations: EPDM is not compatible with petroleum-based products, mineral oils, or grease, which will cause it to fail.
• Types: Both sulfur-cured and peroxide-cured EPDM can be used, though peroxide-cured is generally preferred for better heat resistance and lower compression set.

Common Uses:

• Master cylinder reservoir seals
• Brake caliper seals
• Hydraulic brake system hoses

If you are replacing a gasket for a brake fluid reservoir or related component, EPDM is the correct material. Avoid Buna-N (NBR) or Viton for this specific application, as they are not designed for glycol-based brake fluid compatibility. ”

I do agree EPDM is what I need but when I look for a sheet of it, there is an overload of products/info. Not sure which thickness to buy either.

I am not familiar with that type of master cylinder but, a normal master cylinder does not have any back pressure unless itis some type of air assist. The thickness only needs to be enough to provide a leakproof seal between the 2 mating surfaces because it is not a perfect machined fit. I would assume a 1/16th would be more than plenty. Or possibly even less. Good luck, keep us posted.

Found a piece of EPDM on Walmart Market Place. Wasn’t the easiest, everything I found on eBay was a blend with something else. I’ll find out in a few weeks if it works.

I am late to the party on this but etrailer.com has made my trailer parts/brakes shopping waaaaay easier. Not sure they have what you needed but its my first reference spot for this stuff. I am not affiliated in any way.

They have been for me also except for this matter. Parts are discontinued. They recommended I replace the whole actuator. Terrible suggestion. But I will give them credit for the 2nd time I called about this matter when I found the actuator local and needed a gasket. He also suggested replacing the whole actuator. I mentioned that would be crazy for a gasket… I emailed him pictures and measurements of what I needed. He did try to find something similar in the warehouse.