Stu (post above) has a good guide+video for replacing the ferro fluid. Did mine, fantastic improvement; for very minimal work. Emailed Seas this year; asking if the H1499 DXT was close to the H1054, Seas stated the H1212 was a better match (despite no waveguide). After rebuilding mine, the positive results curbed my interest in replacements, possibly a test of the SEAS Excel T25CF-001 if motivation returns.

808v6, 818.3, G65, G61RSL, G91DH, G08, G98DH, 500v3, 504, 218-LPS, 218, 210, MS200
8000uSE, 5200SE, 5200HSE, DSP5200 (nonSL~fully rebuilt w/ Excel tweeters), DSP3300x2, DSW.2
HD621, Pair of Revivers, AC12