My wife pulled up in the '83 TD and I noticed that something was dripping form the rear right corner. Upon a closer look I discovered that the outer boot was leaking. Is it possible for the grease inside to of thinned out over 20 years, and leak out the boot. Or do I need to look closer at something else. If it is the boot, is this a DIYer and whats involved?

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member