Join Date: Dec 2003
Location: Carson City, NV Class Champion Reno SCCA 2018
Don't know how S3/S4 secondary cylinders compare, but in addition to snap ring issues, you may find the cylinder to be frozen in place, as in my S3 :-(. Added about 2 hours to my replacement exercise. Wish I could recall the removal procedure that worked but thinking it involved lots of penetrating fluid and bad words...believe the bad words finally prevailed.
Also, if your secondary cylinder (aka, slave...don't ask) is shot, it is not uncommon for the primary to fail shortly after secondary replacement, perhaps because of higher pressure in the new unit.
Don't want to make this harder than it needs to be, but I have just replaced the cylinders as a pair.
Steve Waclo Carson City, NV; '87 Spider QV, ES Champion, 2018 Reno SCCA (125k);'93 Honda Nighthawk 750 (105k);'03 GMC Sierra SLE 2500HD Turbo Diesel (155k);'08 Altima Coupe 3.5SE, 6sp (125k)