[Don;t ask where I got this, I"m just passing on information -Ben]

At long last I got a copy of the LRNA bulletin covering drive line clonk in Discoveries and Defenders. My original source never got back to me so I had to go elsewhere. For the record, no, I won't fax you a copy. I've been admonished not to "show" it to anyone. By the way, this problem exists in both manual and automatic transmissions as the bulletin lists replacment part numbers for both.

Here are the salient parts:

Bulletin No: 37/20/96
Subject: Gearbox Mainshaft Spline Wear
Affected Vehicles:

Discovery LJ 178205 onwards
Discovery LJ 506525 onwards
Defender LD 976480 onwards

Detail:

Some customers may complain of clonks and backlash in the transmission system. This may be due to gearbox/mainshaft spline wear. The clonk/backlash will be most apparent in stop/go traffic under overrun conditions or when manuvering the vehicle during parking, etc. From transfer box number 28D 460996 F (Discovery) and 22D 461124 F (Defender) all factory built LT230 transfer boxes have a revised design of input gear, featuring lengthened splines and cross drilled oil feed holes. This modification eliminates the requirement for an oil feed disk (bulletin H415) and eliminates input gear/mainshaft spline fretting/wear. Coincident with this change, the transfer box identification number has been raised to Suffix "F".