I work for a caliper rebuilding company. Silicone grease is not good for use inside the hydraulic system, it is good for lubing slide pins and external components of the caliper that are not subject to intense heat. For the square cut seal and the piston, either clean brake fluid or caliper/wheel cylinder assembly lube is a good choice. The chain stores don't carry this much more but the mom and pop parts houses should have some assembly lube lying around. Silicone grease = silicone dialectric grease, the same as tune-up grease and available at any auto parts store. The #1 problem I see with people rebuilding their own calipers is failure to properly clean the seal groove in the caliper. If everything is clean and the piston surface is in good shape, the caliper will live a long life provided that the correct parts are used to rebuild it, the piston boot remains in good shape, and slide pin lubricant is renewed on a regular basis. A little silicone grease on the inside of the boot helps keep the boot in good shape.