ZDDP (zinc dialkyldithiophosphates) does not prevent wear! It manages wear that the proper engine oil can usually prevent.
It is only emissions related in that the phosporous destroys the oxygen sensor and catalytic converter.
The camshaft wear problem (Huge in Rover Engines) is rooted in the fact
that very few people take the time to understand that a 0W-30 can be thicker and provide better protection than a 10W-40. They simply refuse to educate themselves about the reality of lubrication and instead place all their failt in brand loyalty and meaningless terms like "diesel oil", "synthetic oil" and "racing oil". Not one of them ever bothered to identify the legal definition of "racing oil", "diesel oil" or "synthetic oil". They all end up using low
shear products and then blaming the camshaft failure on the EPA and how they caused a lack of ZDDP!
http://www.ilma.org/resources/ilsac_finalstd011404.pdf
Here is a breifing on Oil Specs. Namly GF-4. ILSAC GF-4 has three components. Engine protection, fuel efficiency and emissions system protection.
The engine protection component only duplicates API SM which fails to meet the minimum requirement of a whole bunch of cars. It falls far far short of the engine protection standards of most proprietary and ACEA ratings (but products labeled ACEA A1 protection actually fail ACEA A1). API SM and ILSAC GF-4 are upgrades in engine protection compared to the older API SL and ILSAC GF-3. Sludge control is one of the areas of improvement but
sludge remains a very significant issue especially in new engine designs with increased combustion chamber acid formation. This includes a significant number of American and Japanese cars. It also is not adequate for the shear
forces in most European cars.
The fuel efficiency standard duplicates the API Energy Conserving standard. It falls short of the fuel efficiency standards of some ACEA ratings, especially during "Soccer Mom" driving conditions.
The Emission system protection standard restricts the sulfated ash, phosphorous and sufur (SAPS) levels. The allowable level is higher for 10W-X0 than for 5W-X0 and 0W-X0 viscosities. The lower the SAPS level, the longer the catalyst and oxygen sensors last. SAPS related contamination is the #1 cause of catalyst failure during warranty. Some ACEA ratings have tighter SAPS limits than ILSAC. Previous ILSAC (GF-1/2/3) and other ratings already
restricted SAPS, zinc, chlorine, etc. ILSAC GF-4 is nothing
more than a continution of that trend.
Rumors have been spread about the failure ILSAC GF-4 and API SM to provide adequate engine protection for certain engines including 1960s era Engines, Like Rovers V8. Some of the ruors are true, others not.
Aftermarket and OEM oil supplements are used and mis-used like crazy. Most include ZPPD. Many include zinc and/or chlorine. Most contain compounds that are not legal to include in a quart of oil but are legal to sell separately.
Many engines (old and new) require much better engine protection than any API or ILSAC rating indicates. Substituting a 10W-40, 15W-40, 20W-50 or even a 10W-30 for the OEM recomended 5W-30 or 5W-20 is NOT a good idea. There is no such thing as an ILSAC approved 10W-40, 15W-40 or
20W-50. Even a 10W-30 will increase the SAPS level and may result in a cheaper base stock. Also, keep in mind also the problem with using the thicker oils, is, weak ring tension does not scrape it off the cylinder walls very good. It is slower to start doing it's lubrication duties on start up.
The high temperature high shear protection required by most newer European cars, some newer American & Japanese cars and some older American and Japanese cars is best met by selection of the OEM product or a proper oil based on the proprietary and/or ACEA ratings, or the product data sheet.
Typical API & ILSAC approval is not enough.