I know it's an old thread but for future reference.
Mastiff air filter:
'Twin Air' filters for the MZ Mastiff,the part no you require is 154512
.......or as I did by luck find the same filter as listed for the KTM SC/Duke and Maico 98/03.
No-Toil air filter maintenance kit - aerosol bidegradable filter oil, filter grease and cleaning fluid (try MX shops
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)