2.) the internal seals were not engineered for continuous exposure to
caustic brake fluid, and as a result, the unit could explode or leak during
use.  Maybe not right away, but eventually, as the fluid attacks the seals
of the garden sprayer.

Mike,

I would question the "caustic" part of the above comment.  Brake fluid is
primarily glycol and is designed to work with synthetic and natural rubber
seals.  What do you think the seals in a garden sprayer are made from?

Jim

The following is quoted from Federal Standard #116,
TITLE 49--TRANSPORTATION
CHAPTER V--NATIONAL HIGHWAY TRAFFIC
SAFETY ADMINISTRATION, DEPARTMENT
OF TRANSPORTATION
PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

"S4. Definitions.
Brake fluid means a liquid designed for use in a motor vehicle hydraulic
brake system in which it will contact elastomeric components made of styrene
and butadiene rubber (SBR), ethylene and propylene rubber (EPR),
polychloroprene (CR) brake hose inner tube stock or natural rubber (NR).
S5. Requirements. This section specifies performance requirements for DOT 3,
DOT 4 and DOT 5 brake fluids; requirements for brake fluid certification;
and requirements for container sealing, labeling and color coding for brake
fluids and hydraulic system mineral oils. Where a range of tolerances is
specified, the brake fluid shall meet the requirements at all points within
the range."

In accordance with the above standards, all brake fluids that meet these
criteria are non-mineral oil based (non-petroleum) by specification. Common
compositions may include synthetic glycol ethers, borate esters, or
silicone.

DOT3, DOT4, SUPER DOT 4, DOT5, DOT5.1 ...ALL of these fluids are tested for
compatibility with all common automotive seal types, including natural
rubber.

Anyone interested in reading the entire Federal Standard #116(or has the
stamina to do so) can find it at the following web site:
http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=49&PART=571&SECTION=116&TYPE=TEXT